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Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Host-finding behaviour of Trichogramma brassicae in maize
    Suverkropp, B.P. - \ 1997
    Agricultural University. Promotor(en): J.C. van Lenteren, co-promotor(en): F. Bigler. - S.l. : Suverkropp - ISBN 9789054857259 - 249
    Chalcididae - Eulophidae - Trichogrammatidae - insecten - plantenplagen - Zea mays - maïs - diergedrag - biologische bestrijding - nuttige insecten - gastheer parasiet relaties - parasitisme - Tortricidae - Ostrinia nubilalis - microlepidoptera - Chalcididae - Eulophidae - Trichogrammatidae - insects - plant pests - Zea mays - maize - animal behaviour - biological control - beneficial insects - host parasite relationships - parasitism - Tortricidae - Ostrinia nubilalis - microlepidoptera
    The potential of natural enemies to suppress rice leaffolder populations
    Kraker, J. de - \ 1996
    Agricultural University. Promotor(en): J.C. van Lenteren; R. Rabbinge; A. van Huis. - S.l. : De Kraker - ISBN 9789054856016 - 257
    insecten - insectenplagen - tortricidae - rijst - oryza sativa - gastheer parasiet relaties - parasitisme - gewasbescherming - biologische bestrijding - cnaphalocrocis medinalis - marasmia - microlepidoptera - insects - insect pests - tortricidae - rice - oryza sativa - host parasite relationships - parasitism - plant protection - biological control - cnaphalocrocis medinalis - marasmia - microlepidoptera

    Rice leaffolders Cnaphalocrocis medinalis and Marasmia spp. (Lepidoptera: Pyralidae) are considered major pests in many Asian countries. Insecticide use against leaffolders is wide-spread, but may not be justified due to tolerance of the rice crop to leaffolder injury and a high level of natural biological control. This study was conducted to obtain more insight in the potential of indigenous natural enemies to suppress rice leaffolder populations and reduce the damage inflicted to the crop. The study started with a descriptive analysis of leaffolder population dynamics in Philippine rice fields, and then concentrated on experimental analysis of egg mortality and the impact of individual predator species. Models were used to integrate the experimental findings, to explain field observations, and to explore the consequences of varying biotic and abiotic conditions for leaffolder population dynamics and damage.

    Rice leaffolder populations in eight unsprayed rice crops were characterized by an egg peak at maximum tillering and a broad larval peak around the booting stage, with peak larval densities ranging from 0.2 to 2.0 per hill. Variation in survival from egg to larval stages between crops was not correlated with the level of egg parasitism, natural enemy abundance, or predator-prey ratios. High levels of N-fertilization resulted in a strong increase in leaffolder larval density and injury, due to a positive effect on egg recruitment and survival of medium-sized larvae. The increase in larval survival was associated with lower predator-prey ratios. Egg mortality in the field a veraged about 60%, and was mainly due to disappearance of eggs and to a lesser extent to parasitism by Trichogramma spp. Non-hatching was of minor importance. The level of egg disappearance was positively correlated with the densities of the predatory crickets Metioche vittaticollis and Anaxipha longipennis. Direct observations confirmed the major role of these crickets: in two crop seasons they were responsible for more than 90% of the observed egg predation. Minor predators were Micraspis sp., Ophionea nigrofasciata, and Conocephalus longipennis. The egg predation rate of the crickets in cages was described adequately with a linear functional response model, indicating that predation was limited only by the search rate. Increasing the predator density per cage led to a decrease in the egg predation rate per capita. Field testing of a model of predation of leaffolder eggs based on cage experiments showed that the observed trend in egg predation could be described as a function of cricket densities and crop leaf area. The evaluation also indicated that predator interference may limit the egg predation rate of the crickets, while the presence of alternative prey did not. A simulation study with a combined model of leaffolder population dynamics and rice crop growth highlighted the importance of natural enemies as well as crop growing conditions. The simulations indicated that larval densities as observed in the unsprayed fields would not cause significant yield loss in a wellfertilized crop. Yield losses simulated with an average leaffolder immigration pattern exceeded economic damage levels when no natural enemy action was included, while introduction of three field-observed natural mortality factors (egg predation, egg and larval parasitism) reduced losses to below these levels. Over their observed range in seasonal abundance, the predatory crickets could reduce leaffolder damage by 5 to 60% (average: 35%).

    The identification of the major egg predators and quantification of their impact can serve as a starting point for research on strategies to conserve natural enemies of rice leaffolders, and as inputs to IPM training programs to stimulate farmers to reduce insecticide sprays against rice leaffolder. The study also indicated the importance of optimization of nitrogen fertilization to avoid reliance on chemical control, by maximizing the positive effects on yield formation and tolerance to injury, while minimizing the leaffolder density response. For this purpose, a combined leaffolder-rice simulation model is a useful, integrative tool, to study how interaction between these mechanisms affects rice yield.

    Hunting for hiding hosts : the behavioral ecology of the stemborer parasitoid Cotesia flavipes
    Potting, R.P.J. - \ 1996
    Agricultural University. Promotor(en): J.C. van Lenteren; L.E.M. Vet. - S.l. : Potting - ISBN 9789054855514 - 125
    Ichneumonidae - parasieten - dieren - voedingsgedrag - insecten - insectenplagen - Tortricidae - biologische bestrijding - nuttige insecten - Chilo partellus - stengelboorders - microlepidoptera - Ichneumonidae - parasites - animals - feeding behaviour - insects - insect pests - Tortricidae - biological control - beneficial insects - Chilo partellus - stem borers - microlepidoptera

    Classical biological control involves the introduction of an exotic natural enemy to control an introduced pest species. In 1991 the department of Entomology of the Wageningen Agricultural University started a collaborative project with the International Centre for Insect Physiology and Ecology (ICIPE) in Nairobi Kenya, on the biological control of stemborers in Africa. The gregarious endoparasitoid Cotesiaflavipes (Hymenoptera: Braconidae) was chosen as the natural enemy to be introduced against the accidentally introduced pest Chilopartellus (Lepidoptera: Pyralidae) in East-Africa (Overholt et al., 1994; Omwega et al., 1996). The research described in this thesis was related to this project and addressed several aspects of the behavioral ecology of this parasitoid. In the first part, gaps in the knowledge on behavioral ecology of C.flavipes are studied which include the longand short-range searching behavior, some aspects of the life history and host discrimination abilities. The second part focuses on the intraspecific variability in C.flavipes behavior and here we determine to what extent the reported plant and host specificity in C.flavipes has a genetic basis or is due to phenotypic plasticity through learning.

    Micro-habitat and host location in Cotesiaflavipes

    The first part addresses the origin of the olfactory stimuli involved in hostmicrohabitat location (chapter 2) and the contact stimuli involved in tunnel and host location on a stemborer infested plant (chapter 3). In chapter 2 it is demonstrated that a major source of the attractive volatiles from the plant-host- complex is the stemborer-injured stem, including the frass produced by the feeding larvae. Moreover, the production of volatiles attractive to a parasitoid is not restricted to the infested stem-part but occurs systemically throughout the plant. The uninfested leaves of a stemborer-infested plant emit volatiles that attract female C.flavipes . An exogenous elicitor of this systemic plant response is situated in the regurgitate of a stemborer larva. When a minor amount of regurgitate is inoculated into the stem of an uninfested plant, the leaves of the treated plant emit volatiles which attract female C.flavipes . Evidence is accumulating that plants are actively involved in attracting natural enemies Dicke 1994). However, whether plants have specifically evolved the ability to release volatiles that attract natural enemies of the herbivore that is attacking them remains a matter of debate (Bruin et al. 1995).

    Foraging behavior on stemborer infested plant

    Once a female C.flavipes has located a stemborer infested plant, it has to locate the concealed host inside the plant stem. In chapter 3 the behavior of female C.flavipes on stemborer infested plants was investigated. It is demonstrated that larval frass, caterpillar regurgitate and holes in the stem are used in host location by C.flavipes . After locating the exit hole of the stemborer tunnel, where larval frass has accumulated, the parasitoid female tries to enter the stemborer tunnel. This can take a long time because the tunnel is often blocked by larval frass and the female sometimes has to squeeze through small holes. The response to host products by C.flavipes seems not to be host species specific. Female C.flavipes respond to frass from four different stemborer species and one leaf feeder. No differences are found in the behavior of C.flavipes on maize plants infested with the suitable host, Chilopartellus (Lepidoptera: Pyralidae), or the unsuitable host, Busseola fusca (Lepidoptera: Noctuidae). Attacking a concealed stemborer larvae in the confined space of stemborer tunnel is not only time consuming but also risky. It is demonstrated that 30-40% of the parasitoids is killed by the spitting and biting stemborer larva. Takasu and Overholt (1996) showed that a female parasitoid has a high probability (0.9) to be bitten to death when it approaches the host towards the head. However, the majority of the females were first able to successfully parasitize its offensive host before being killed. A female C.flavipes needs only a few seconds to inject around 45 eggs into its host. The high probability of mortality at each host encounter results in a very low expectation of the number of lifetime host encounters. The possible consequences of this low lifetime host encounter rate for the evolution of life history- and foraging strategies formed the basis of a large part of this thesis.

    Life history ofCotesiaflavipes

    C.flavipes is relatively short lived: without food the parasitoids die within two days, with food and under high humidity conditions they die within 5-6 days. In chapter 3 the fecundity and clutch size allocation of C.flavipes was investigated. It is demonstrated that C.flavipes is pro-ovigenic and has around 150 eggs available for oviposition. In the first encountered hosts 35-45 eggs per host are laid. Thus, a relatively large proportion of the available egg load (20-25%) is allocated to each host, and a female C.flavipes is equipped with an eggload to parasitize 3-4 hosts only. Especially for animals whose lifetime reproductive success is limited by opportunities to reproduce, clutch size theory predicts a maximization of the fitness gain per clutch (Godfray, 1987). This may be true for C. flavipes, which has a short lifespan and a high mortality risk at each host encounter, resulting in a low number of expected lifetime host encounters (Chapter 3). In chapter 4 it is demonstrated that the number of produced adults from superparasitized hosts is equal to that of singly parasitized hosts. This indicates that female C.flavipes indeed lay an optimal clutch size in fourth instar C. partellus larvae.

    Host- and host-sitediscrimination

    The fitness consequences of superparasitism and the mechanism of host discrimination in Cotesia flavipes are described in chapter 4 . Naive females readily superparasitized and treated the already parasitized host as an unparasitized host by allocating the same amount of eggs as in an unparasitized host. However, there was no significant increase in the number of emerging parasitoids from superparasitized hosts due to substantial mortality of parasitoid offspring in superparasitized hosts. Furthermore, the developmental time of the parasitoids in a superparasitized host was significantly longer than in a singly parasitized host and the emerging progeny were significantly smaller (body length and head width). Naive females entered a tunnel in which the host was parasitized 4 hours previously and accepted it for oviposition. Experienced females (oviposition experience in unparasitized host) refused to enter a tunnel with a host parasitized by herself or by another female. In experiments where the tunnel and/or host was manipulated it was demonstrated that the female leaves a mark in the tunnel when she has parasitized a host. The function of the avoidance of superparasitism. in C.flavipes is clear: a discriminating female saves searching time, avoids the wastage of eggs and avoids a direct mortality risk. The mechanism of host discrimination is the recognition of a chemical mark on the tunnel substrate.

    The role of learning in hostforaging

    Many studies have shown that parasitoids can learn visual or olfactory stimuli associated with successful host location and use these odours in subsequent foraging decisions (reviewed by Turlings et al., 1993; Vet et al., 1995). The ability to learn has now been demonstrated in more than 20 different parasitoid species and learning in parasitoids seems to be the rule rather than the exception (Turlings et al., 1993). In chapter 5 the role of learning in host foraging in C.flavipes was investigated. Using experimental procedures similar to other parasitoid learning studies, the role of the learning mechanisms priming (i.e. increase in response) and preference-induction in the foraging of C.flavipes was determined. No evidence was found that C.flavipes uses odour learning in hostmicrohabitat location. There was no significant effect of the development and emergence environment on the response level or preference towards infested plant odours. Neither was any evidence found that experience with a particular plant-host-complex during foraging influences subsequent foraging decisions in C.flavipes females.

    Recent discussions of animal learning emphasize the importance of considering an animals ecology when studying and interpreting its learning abilities. Recently, it has been hypothesized that the adaptive value of learning in foraging is dependent on the predictability of the environment (Stephens, 1993) and the number of lifetime foraging decisions (Roitberg et al., 1993). Learning is not expected when the foraging environment is highly predictable (i.e. the resource is constant) and when animals make only a few decisions while foraging. Taking the ecology of C.flavipes into account it is hypothesized that two factors may be responsible for the lack of learning in foraging in C.flavipes : a predictable foraging environment and the restricted number of lifetime foraging decisions.

    EVOLUTION OF LIFE HISTORY AND FORAGING STRATEGIES

    Evolutionary ecological theory concentrates on the interpretation of form and function of individuals as adaptations to their environment. Theories of life history evolution predict what sorts of life history should evolve in specified ecological circumstances (e.g. Steams, 1992; Roff, 1992) and optimal foraging theory addresses the problem of choice among resources or habitats (e.g. Krebs and Davies, 1981; Stephens and Krebs, 1986). It is tempting to relate the ecology of C.flavipes with its life history characteristics and its foraging tactics. The stemborer parasitoid C.flavipes has a peculiar ecology. It not only forages for hosts in a relatively homogeneous and predictable habitat, but it also has a risky attack tactic resulting in a low number of expected lifetime host encounters.

    The small C.flavipes attacks stemborer larvae by entering the stemborer tunnel (chapter 3). To reach the host, the parasitoid female has to squeeze through small holes in the tunnel which is filled with larval frass. It has been suggested that the dorso-ventral body shape, which is typical of the Cotesia species belonging to the Cotesiaflavipes complex is an adaptation to this ingress behavior (Kimani, pers. comm.). Attacking a host in the confined space of a stemborer tunnel is not without risk for the female parasitoid. At each host attack the female has a considerable risk to be killed by its aggressive host (chapter 3). The short oviposition time (around 40 eggs in 3-4 seconds) may be an adaptation to this mortality risk. The majority of the females that are killed have already successfully parasitized their host.

    The relatively high mortality risk at each host encounter in combination with the short lifespan results in a very low number of expected lifetime host encounters. This is reflected in the eggload of a female at emergence, which is just enough to parasitize 3-4 hosts (chapter 3). When the probability of surviving to find another host is small, optimal progeny allocation models predicts an optimal 'Lack' clutch size, where fitness is maximized per host (Waage & Godfray, 1985; Godfray 1987). Although it was not tested in depth the results of the superparasitism experiments (chapter 4) indicated that C.flavipes lays an optimal clutch size.

    The foraging environment of a female C.flavipes can be envisaged as a homogeneous and stable habitat, consisting of a field of perennial grasses with a few prevalent stemborer species. In chapter 5 it is hypothesized that this predictable foraging environment together with the low number of expected lifetime host encounters plays a part in the absence of (odor) learning in C.flavipes host foraging. In chapter 4 it is demonstrated that female C.flavipes leave an external mark on the tunnel substrate after parasitization. It is generally hypothesized that marking evolved as a means for individuals to avoid superparasitizing hosts they themselves previously parasitized (Roitberg and Prokopy, 1987). A female C.flavipes saves time and avoids a superfluous mortality risk by avoiding utilized host tunnels.

    When a parasitoid has a high mortality risk at each oviposition, life history theory predicts a high selectivity to avoid waste of progeny (Iwasa et al., 1984; Ward, 1992). The parasitoid should not risk her life for low quality hosts, such as unsuitable hosts or already parasitized hosts. However, naive female C.flavipes (no oviposition experience) seem to have a very opportunistic host selection behavior. In chapter 3 it is demonstrated that C.flavipes did attack the (new) unsuitable host B. fusca and in chapter 5 it is found that naive females did utilize a previously parasitized host. The lack of an innate ability or willingness to avoid low quality hosts in C.flavipes may be due to the constrained opportunities to find and parasitize hosts. Each animal faces a evolutionary trade off between reproducing now or in the future, whereby survival chances play a determining role. The best strategy for a recently emerged naive female C.flavipes is to accept the first encountered host, irrespective its quality. Superparasitism pays when future expectancy of host encounter rate is very low. The lower fitness increment of superparasitism (in comparison with single parasitism) will always outweigh the fitness penalty of not finding any unparasitized host.

    In chapter 5 it is demonstrated, however, that females with oviposition experience do avoid previously utilized stemborer tunnels. The increased choosiness after an oviposition experience in an unparasitized host may be due to the fact that, the parasitoids assessment of host availability has changed. When there is a high chance of finding unparasitized hosts it does pay to reject. Furthermore, in contrast to naive females, oviposition experienced females that superparasitize run the risk to encounter a host they themselves previously parasitized (Van Alphen and Visser, 1990). A safe strategy of females that have already parasitized one or more hosts may be to avoid any already parasitized host to avoid competition among her own progeny.

    VARIATION IN PARASITOID BEHAVIOR AND BIOLOGICAL CONTROL

    In biological control the performance of a released parasitoid population in the field is dependent on the ability of individual females to locate hosts. The behaviour of parasitoids is not fixed and predictable, but most of the times highly variable. This variation in behaviour can be an obstacle in the effective use of natural enemies in biological control, so it is necessary to understand the sources of variation in behavior (Vet et al., 1990; Lewis et al., 1990). In this way we can predict the general behavior of the natural enemy population in the field better and we may even be able to manipulate it.

    Behavioral variation may exist because individuals differ genetically in propensity to find or accept different hosts. Secondly, individuals may differ because they have experienced different environments (i.e. learning).

    Local variation in parasitoid behavior and physiology

    The existence of plant specific strains in C.flavipes has been postulated by Mohyuddin and coworkers (e.g. Mohyuddin et al., 1981; Mohyuddin, 1990). However, the genetic and/or phenotypic basis for this reported specificity has never been addressed thoroughly. For instance, early adult conditioning can mimic genetic differences between parasitoid strains. However, in chapter 5 we demonstrated that there is no early adult conditioning for the development and emergence environment in C.flavipes , indicating innate (genetic) differences among strains. Therefore, the between population variation in behavior and physiology of C.flavipes populations was investigated in more detail in chapter 6 . The host selection behavior and physiological compatibility with different stemborers (i.e. parasitoid virulence) was compared for six different geographic strains of C.flavipes that differed in the plant-host-complex they were obtained from. The results of these host selection experiments indicated that there is no interspecific variation in host selection behavior among C.flavipes strains, which contradicts the finding of the Mohyuddin research group. However, the comparative experiments did show variation in reproductive success among strains. The most significant result was that the strain with the longest co- existence time with the new host D. saccharalis , had the highest reproductive success on this host species. It is argued that the earlier reported existence of C.flavipes strains is not based on a differential host selection behavior, but on differences in physiological compatibility between local parasitoid and host population. C.flavipes has been

    used on a worldwide scale in biological control against stemborers with varying degree of success (Polaszek and Walker, 1991). The failure of biological control with C flavipes may be due to the introduction of an inappropriate strain. The present study has demonstrated that there is no differential plant preference among strains, but that there are differences in parasitoid virulence among strains. For a reliable biological control with C flavipes it is thus important to select a strain that is physiologically adapted to the target host population.

    Analysis of the sex pheromones of Symmetrischema tangolias and Scrobipalpuloides absoluta
    Griepink, F.C. - \ 1996
    Agricultural University. Promotor(en): Æ. de Groot; J.H. Visser; T.A. van Beek. - S.l. : Griepink - ISBN 9789054855736 - 132
    feromonen - tortricidae - insecten - plantenplagen - analyse - chemie - microlepidoptera - analytische scheikunde - pheromones - tortricidae - insects - plant pests - analysis - chemistry - microlepidoptera - analytical chemistry

    Sex pheromones are substances which are used by insects to attract a partner with the intention to mate. Pheromones are essential for the species survival because without them the partner cannot be located. When the chemical structures are known, the sex pheromones could be applied for pest control of that species. Sex pheromones are produced by the insect itself and they are attractive in very low concentrations. The development of resistance against sex pheromones, in contrast to pesticides, is considered unlikely. Owing to the species specificity and the low amounts necessary, the natural environment of the pest is less afflicted by the use of sex pheromones in comparison to conventional pesticides.

    This thesis describes the isolation, identification and possible applications of the sex pheromones of two South-American moths, Symmetrischema tangolias and Scrobipalpuloides absoluta . The research was carried out as a co-operative project between the Research Institute for Plant Protection (IPO-DLO), Wageningen, The Netherlands, the Department of Organic Chemistry of the Wageningen Agricultural University (OC-WAU) and the International Potato Center, Lima, Peru (CIP). The project was financially supported by the Netherlands' Minister for Development Co-operation.

    The moth Symmetrischema tangolias (Gyen), synonym: Symmetrischema plaesiosema (Turner), occurs mainly in the higher regions of the Andes in Peru and Bolivia where it is a severe pest of potatoes. The larva lives in the fields in the stems of potato plants and in storage places in the tubers. The harvested potatoes are stored in open facilities which are easy accessible to the insects. The potato growing is essential for the local food provision in the above-mentioned areas.

    The sex pheromone of Symmetrischema tangolias has been identified (chapter 3) as a 2: 1 mixture of (E,Z)-3,7-tetradecadienyl acetate ( 6 ) and (E)-3-tetradecenyl acetate ( 1 ). In the sex pheromone glands, two additional minor, to the sex pheromone related, compounds have been identified, namely (Z)-5-tetradecenyl acetate (25) and (Z)-7-tetradecenyl acetate ( 26 ) (figure 8.1). The ratio of these compounds in the sex pheromone gland is: 63 : 31 : 5 : 1 for 6 : 1 : 26 and 25 respectively.

    In a new wind tunnel at IPO-DLO, several mixtures of the identified and synthesised sex pheromone components have been tested in different ratios (chapter 6). A mixture of 6 and 1 appears to be more attractive than the two components separately. Mixtures of 6 and 1 in ratios of 1 : 1 and 2: 1 are equally attractive. The addition of small amounts of minor components 25 and 26 does not affect the attractiveness of the sex pheromone blend. The function of these two minor components therefore remains unclear.

    The amounts and ratios of the four gland constituents were measured during the 24-hrs dark- light cycle (chapter 4). A new approach was followed which involved the direct introduction of sex pheromone glands into the gas chromatograph (GQ by using a special temperature programmable GC-injector. With this method it was possible to examine glands without prior processing which provides a clear advantage over earlier described methods. It turns out that the total amount of sex pheromone in the glands varied strongly from individual to individual (3.8 - 350 ng/♀). The total sex pheromone amounts were significantly lower in the scotophase than in the photophase (62.2 and 101.5 ng/♀respectively). The ratios of the various gland constituents showed a symmetrical distribution which did not fluctuate during the 24-hrs dark-light cycle.

    The synthetic sex pheromone was highly attractive to male Symmetrischema tangolias in field tests conducted in potato fields and in storage facilities in Peru. The local farmers were exited about the results and wish to apply the sex pheromone as soon as it becomes available. Although the synthesis of the mono-unsaturated compound 1 is easy, large scale synthesis of the double-unsaturated compound 6 (which has been never reported before) is problematic.

    The moth Scrobipalpuloides absoluta (Meyrick), synonym: Scrobipalpula absoluta (Meyrick), lives in low altitude areas of South America. The larva is a leafminer of tomatoes and has developed into a devastating pest in tomato cultivation, especially in Brazil, Peru and Chile. In contrast to small-scale potato crops in higher parts of the Andes, the tomato growing is a large-scale and professional business. The harvested tomatoes are largely processed and exported. Therefore, tomato growing is of national economic interest for the involved countries.

    The sex pheromone of Scrobipalpuloides absoluta has been identified (chapter 5) as a 9: 1 mixture of (E,Z,Z)-3,8,11-tetradecatrienyl acetate ( 16 ) and (E,Z)-3,8- tetradecadienyl acetate ( 3 ) respectively (figure 8.2).

    The ratio of these two identified compounds in the sex pheromone gland is 92: 8 (for 16 : 3 respectively). On a Peruvian tomato farm, several mixtures of the identified compound were tested in ratios between 100 : 0 and 80 : 20, for 16 : 3 respectively. All tested mixtures turned out to be highly attractive to Scrobipalpuloides absoluta males, however, none of them appeared superior. Both the identified sex pheromone components 16 and 3 are unique to this species. The synthesis of the minor compound 3 can be increased easily, however, large-scale synthesis of 16 may provide more problems due to its three double bonds.

    Various techniques were used to identify the sex pheromones of Symmetrischema tangolias and Scrobipalpuloides absoluta. By means of GC, the chain lengths, functional groups and number of double bonds could be established. The active components were found in the gas chromatogram by means of electroantennography (EAG-detector). This detection technique is based on the application of the insect's antenna (olfactory organ) as a detector. From the gas chromatographical research it turned out that the sex pheromone candidates for both species belonged to the same group of linear unsaturated compounds all with a chain length of 14 carbons. The mono-unsaturated components 1 , 25 and 26 could be identified with related reference compounds which were all available at IPO-DLO. Of the double-unsaturated compound 6 of the Symmetrischema tangolias sex pheromone sufficient amounts could be isolated by means of preparative GC to unambiguously determine the (E)-3-double bond with NMR. Through EAG-recordings of all mono-unsaturated related compounds the (Z)-7-double bond was postulated as the other double bond in molecule 6 . The synthesis of 6 confirmed the postulated structure. By means of derivatisation of sex pheromone compounds with dimethyl disulphide (DMDS) subsequently followed by analysis of the derivatives obtained with mass spectrometry, the double bond positions in the mono- and double-unsaturated compounds could be determined directly. For compound 3 the two double bonds could be located at positions 3 and 8 with the DMDS method. All four possible (E/Z) isomers were synthesised, tested with EAG-recordings and compared to the analytical obtained data on the minor sex pheromone component of Scrobipalpuloides absoluta. Through this the identity of 3 could be confirmed. With the DMDS derivatisation technique two of the three double bonds in 16 could be unambiguously located at positions 3 and 8, similar to the minor component 3 . The obtained EAG results suggested the same E/Z configuration for these two double bond positions in 16 . GC-analysis of available mono- and polyunsaturated related compounds left three possibilities for the structure of 16 . The identity of 16 was determined through synthesis of all three possibilities and comparison of the analytical data with the data obtained for the sex pheromone compound.

    A closer investigation of the DMDS derivatives of these latter three triple-unsaturated compounds revealed the possibility for the direct determination of all three double bond positions solely through interpretation of mass spectra. This has not been reported before for these types of molecules. For this reason, and because of its importance for this kind of research, a separate chapter (chapter 2) was dedicated to it.

    The discussion contains a proposal for the biosynthetic formation of the identified sex pheromones. Also the price control in commercial synthesis of sex pheromones is mentioned and illustrated through an example. Both pheromones of Symmetrischema tangolias and Scrobipalpuloides absoluta contain a synthetically problematic compound. Considering the need for these sex pheromones it is recommended to continue the research for more efficient synthetic routes.

    Onderzoek naar de verspreiding van de anjerbladroller, Cacoecimorpha pronubana (Huebner), in Nederland, vooral in het Zuidwesten, gedurende 1994
    Woets, J. - \ 1995
    Wilhelminadorp : Proefstation voor de Fruitteelt
    insecten - plantenplagen - tortricidae - tuinbouw - plantenziekten - epidemiologie - distributie - nederland - microlepidoptera - insects - plant pests - tortricidae - horticulture - plant diseases - epidemiology - distribution - netherlands - microlepidoptera
    De kleine vlinders : Handboek voor de faunistiek van de Nederlandse Microlepidoptera
    Kuchlein, J.H. ; Donner, J.H. - \ 1993
    Wageningen : Pudoc - 715
    dieren - zoögeografie - fauna - handboeken - identificatie - lepidoptera - nederland - tortricidae - wildbescherming - microlepidoptera - animals - zoogeography - fauna - handbooks - identification - lepidoptera - netherlands - tortricidae - wildlife conservation - microlepidoptera
    Parasites of Lepidopteran stemborers of tropical gramineous plants.
    Jr. Smith, J.W. ; Wiedenmann, R.N. ; Overholt, W.A. - \ 1993
    Nairobi : ICIPE Science Press - ISBN 9789290640561 - 89
    nuttige insecten - biologische bestrijding - graansoorten - voedselgewassen - insecten - noctuidae - insectenplagen - tortricidae - tropen - stengelboorders - microlepidoptera - stem borers - beneficial insects - biological control - cereals - food crops - insects - noctuidae - insect pests - tortricidae - tropics - microlepidoptera
    Trail marking and following by larvae of the small ermine moth Yponomeuta cagnagellus
    Roessingh, P. - \ 1989
    Agricultural University. Promotor(en): L.M. Schoonhoven. - S.l. : Roessingh - 117
    Tortricidae - insecten - larven - communicatie tussen dieren - geurstoffen - feromonen - Yponomeuta cagnagellus - microlepidoptera - rupsen - Tortricidae - insects - larvae - communication between animals - odours - pheromones - Yponomeuta cagnagellus - microlepidoptera - caterpillars

    The importance of chemical cues in insect behaviour is well established (Bell & Cardé, 1984). The best known examples include the sex pheromones of butterflies and moths, and the aggregation pheromones of bark beetles. In eusocial insects (bees, wasps, ants, and termites) pheromones are widely used to maintain the organization of the colony. Many of these species produce chemical markers (trail pheromones) and deposit them on terrestrial trails that lead to food sources or nesting sites. Trail pheromones may also serve as cues in home range orientation and can facilitate migration of colonies (Attygalle & Morgan, 1985). However, trail following is not confined to eusocial species and is, for instance, also found in the Lepidoptera. Fabre (1922) already described the striking following behaviour of the procession caterpillar Thaumetopoea pityocampa (Denis & Schiffermüller). To explain his observations, he stressed the importance of tactile stimuli from the silken treads that these (and other) caterpillars produce, and that can be followed. Although this argument still holds today (Chapter 2), it has become clear that, in addition to silk, chemical trail markers may also be important in the social behaviour of caterpillars (Fitzgerald & Peterson, 1988). The best documented examples are found in the Lasiocampidae. In Eriogaster lanestris trail marking was demonstrated by Weyh & Maschwitz (1978), and in the genus Malacosoma chemical trails convey information about the quality of a feeding site, and recruit other larvae to these places (Fitzgerald & Peterson, 1983: Peterson, 1988). In spite of these thoroughly studied examples, knowledge about chemical communication in caterpillars is limited, and mainly restricted to the Lasiocampidae. To gain more insight in trail following and trail marking in the Lepidoptera it is necessary to study this behaviour in other families.

    This thesis focuses on caterpillars of small ermine moths, members of the genus Yponomeuta. This group has been studied in the context of a long term multi-disciplinary research program on speciation, and host plant selection is thought to be an important element in the speciation process (Wiebes, 1976). Food preferences of larvae are related to host preferences of female moths. This makes it interesting to see whether speciation is accompanied by interspecific differences in larval trails to feeding sites.

    There are additional reasons to investigate trail marking and following in the Lepidoptera. Caterpillars have been advocated as model systems in the study of feeding behaviour (Schultz, 1983; Schoonhoven 1987), in part because their behaviour is relatively simple. A caterpillars primary function, gathering as much food as possible, is not complicated by tasks such as mate finding or taking care of offspring. In addition the sensory system is limited. Only about 90 chemosensory cells function in translating chemical messages from the environment into signals for the central nervous system (Albert, 1980; Devitt & Smith, 1982; Schoonhoven,1987). In spite of this restricted number of input channels, caterpillars can display striking food preferences, and will often die from starvation, rather than accept a non-host plant. Such behaviour, together with the possibility of tracing sensory connections into the central nervous system (Kent & Hildebrand, 1987) make caterpillars a good choice for studying the relationship between neurophysiology and behaviour.

    A further point of interest is the possible integration of sensory information. The receptors for sex pheromones are in general separated from those that perceive stimuli associated with food. Trail pheromones of caterpillars bear a close relation to food finding. Therefore these insects may have an integrated receptor system that responds to both food and trail pheromone stimuli.

    The objectives of this study were (1) to determine whether trail pheromones are employed by Yponomeuta and, if so, whether they differ in different species, (2) To identify receptors responsible for pheromone detection, and (3) to determine whether these receptors operate in an integrated way with receptors for food perception. However, as a first step in the analysis of this system basic knowledge must be gained about trail following behaviour itself, the chemicals involved, the senses used and the oecological context in which it functions. These questions form the main topics of this thesis.

    Most experiments were performed on larvae of Y. cagnagellus (Hübner) (Fig. 1). This species is common in the Netherlands and suitable for behavioural studies. In addition, the caterpillars are gregarious throughout their development, suggesting that they may use a trail marker. Malacosoma caterpillars were used in some experiments to allow comparison to a species with well defined trail following behaviour, and an identified trail pheromone.

    Outline of the thesis

    Trail following in Y. cagnagellus

    The study begins by asking whether Y. cagnagellus in fact exhibits trail following behaviour (chapter 2). Two-choice tests on filter paper Y-mazes show clearly that this is the case. In addition it is demonstrated that a tactile component of the trail (the silk) can be used as a cue. Y. cagnagellus does not discriminate between its own trails and those of 5 other Yponomeuta species, but does prefer its own trails over those of M. neustria . This lack of species specificity within the genus is, in contrast to sex pheromones, not uncommon for trail pheromones, possibly because the relationship between mating success and the signal is indirect.

    A chemical marker

    The existence of trail following behaviour does not by itself prove that a chemical marker is involved. Evidence for the presence of a chemical signal is presented in chapter 4. The marker appears to be water soluble, and highly stable under laboratory conditions. Behavioural responses to extracts from several glands and body parts show that the marker is present in the labial glands (the silk gland) only. Therefore, the marker is probably secreted with the silk.

    The receptors involved in trail following behaviour

    Chapter 3 describes the sensory organ used for the perception of the trail. In this chapter a comparison is made with the American tent caterpillar Malacosoma americanum, a known trail follower (Fitzgerald, 1976). Chemoreceptors in caterpillars are located on the antennae, the maxillary palps, the galea and on the inner side of the labrum (Fig. 1). Systematic removal of various relevant structures shows that the maxillary palps are necessary for the detection of the trail in both M.americanum and Y.cagnagellus. Since the source of the trail marker, as well as its chemical composition, differs between the two species, this is most likely an example of convergence of chemoreceptor function.

    Although the maxillary palps contain olfactory as well as gustatory receptors, the trail markers seem to be perceived only by contact chemoreception. This follows from the observation that trails covered with fine nylon mesh do not elicit any response. Moreover the long lifetime and stability of the markers, suggest that they have a low volatility.

    Electrophysiology of the maxillary palp

    Although the palps house a considerable fraction of the sensory equipment of a caterpillar (30-40 cells, more than 1/3 of the total), only very little is known about these organs. Therefore an electrophysiological survey of the chemoreceptors was conducted (Chapter 5). Because the sensilla are too small for tip recording, gustatory stimuli were applied to the whole tip of the palp. Electrical activity of only a few cells at a time was recorded with a glass microcapillary electrode. To aid analysis, a computer program was developed (Chapter 7). Following the ideas of van Drongelen et al. (1980), the program was designed to be highly interactive and to function as both as a display- and manipulation tool.

    Plant volatiles were used as olfactory stimuli (terpenoids and C6 fatty acid derivatives or 'green odours', Visser & Avé, 1978). These were chosen in part on the basis of the results from a dynamic headspace analysis (Cole, 1980) of Euonymus europaeus , the host of Y. cagnagellus . Silk extracts and salt solutions were employed as gustatory stimuli. Evidence was found for the existence of two groups of olfactory receptor cells, sensitive to (E)-2-hexenal and hexanal (aldehydes) or to (Z)-3-hexen-1-ol and 1-hexanol (alcohols). Receptors responsive to the silk extracts (and probably to the trail pheromone) were also identified. These cells do not show the degree of specificity typical of cells specialized for lepidopteran sex pheromones but, rather, resemble the generally more broadly tuned receptors for food components.

    The results from this and the preceding chapters strongly suggest the existence of a chemical trail marker in Y. cagnagellus , secreted with the silk and detected by contact-chemosensory neurons housed in the maxillary palps.

    Oecological and evolutionary aspects

    Chapter 6 addresses the the oecological and evolutionary relevance of such a signal. In eusocial insects as well as in Malacosoma , trail pheromones are often used to recruit siblings to high quality feeding sites (Peterson, 1988). In Y. cagnagellus this does not happen, but field observations have shown that a groups of caterpillars moves its silken nest over considerable distance, on average four times during development. The trail marker could help to maintain gregariousness during these migrations. Thus, it is of interest to ask whether gregariousness is advantageous. While many authors have discussed the benefits of larval aggregation (e.g. Tsubaki, 1981; Fitzgerald & Peterson, 1988; Weaver, 1988), gregariousness may also be associated with distinct disadvantages, for instance those arising from competition for food (Charnov et al., 1976). In chapter 6 a simple evolutionary model is presented to analyze the influence of these conflicting parameters on the evolutionary stability of gregarious behaviour. One result from this study is that it would be informative to classify larval behaviour in terms of the time of which larvae switch from gregariousness to solitary food searching.

    Integrated pest management in apple orchards in the Netherlands : a solution for selective control of tortricids
    Reede, R.H. de - \ 1985
    Landbouwhogeschool Wageningen. Promotor(en): J.C. van Lenteren, co-promotor(en): L.H.M. Blommers. - Wageningen : De Reede - 103
    appels - biologische bestrijding - insecten - malus - nederland - plantenplagen - gewasbescherming - tortricidae - microlepidoptera - apples - biological control - insects - malus - netherlands - plant pests - plant protection - tortricidae - microlepidoptera
    Field trials to compose a coherent system of Integrated Pest Management (IPM) for apple orchards in the Netherlands were started in 1967, when the 12 ha apple orchard "De Schuilenburg" at Kesteren became available for experiments on IPM. Natural control of one of the most severe pests under conventional control, the fruit tree red spider mite Panonychus ulmi , is a central part in IPM. Many broad-spectrum pesticides exterminate the predacious mite Typhlodromus pyri , which is responsible for the natural control in IPM in the Netherlands. Only selective agents are applied, therefore, against pests which are not, or only partially, naturally controlled, preserving T. pyri and other useful arthropods.

    The aim of the present study was to investigate the feasibility of the following selective compounds for leafroller control in IPM in apple orchards: (a) a bacterial agent, Bacillus thuringiensis (Dipel), (b) a chitine synthesis inhibitor, diflubenzuron (Dimilin) and (c) insect growth regulators (IGR) with juvenile-hormone activity, epofenonane and fenoxycarb.

    Initial studies were carried out at the experimental orchard "De Schuilenburg", in 0.5-1.0 ha plots, for five consecutive years. The degree of leafroller fruit damage in untreated plots ranged from 5 to 13%; this damage was caused by a complex of leafroller species. Adoxophyes orana was most abundant in the summer, whereas Spilonota ocellana , Pandemis heparana and Hedya nubiferana were dominant in the spring. Under Dipel regimes, both the total leafroller population and the leafroller fruit injury were halved. Dipel was relatively ineffective against P.heparana, H. nubiferana and, in particular, S. ocellana . Dimilin also halved leafroller fruit injury. This compound was very effective against S. ocellana , H. nubiferana and Archips podana . Dimilin, however, did not affect A. orana and the population of P. heparana was only reduced to about one-third of the blanco value. Leafroller control with epofenonane, which was applied twice in the spring, was not succesful. This may be due to reinfestation from the untreated plots, which lay adjacent to the treated plots in our experimental set- up. Dipel, Dimilin and epofenonane did not appear to affect the level of parasitism of A. orana by Colpoclypeus florus . However, in this respect the standard plots, treated with broad-spectrum insecticides, gave similar results, so no firm conclusion can be drawn.

    A second series of experiments concerned the effect of fenoxycarb and epofenonane. Apple trees were either artificially infested with A. orana and P. heparana or harboured several naturally occurring leafroller species. The caterpillars were restricted in gauze-bags on leaf-clusters after the apple trees had been sprayed once or twice, and the morphogenetic effect was observed. Fenoxycarb was effective at a concentration about 10 times lower than that of epofenonane. The foliar residue of fenoxycarb remained active for at least 4 weeks. Laboratory experiments indicated that although the foliar residue of epofenonane caused severe morphogenetic effects on the host A. orana, the ectoparasite Colpoclypeus florus completed its development on the host. When the host and parasite were exposed to fenoxycarb, however, the parasite often died at the pupal stage. Similar experiments with the endoparasite Apanteles ater in the host Archips rosana did not reveal higher mortality of the parasite than in the control.

    In a following study, large-scale application of fenoxycarb and epofenonane in various IPM apple orchards were tested for several consecutive years. The IPM orchards were carefully selected to include IPM orchards adjacent to conventionally sprayed orchards, and IPM orchards well isolated from other orchards. The population of the leafroller species as well as the leafroller fruit injury level could be kept low by spraying twice in spring, irrespective of the location of the orchard. Reinfestation from adjacent orchards, if it occurred at all, played only a minor role in the final effect.

    The determination of the timing of epofenonane and fenoxycarb required sampling of larvae and periodical observations on the larval stage. In order to facilitate the timing simulation models were developed to predict the emergence of the last instar of P.heparana and A. orana in the field. These models were based on laboratory experiments and on data from the literature and included only the temperature as a driving variable. The simulated curves of emergence of last-instar larvae, pupae and adults corresponded well with the field observations. To investigate whether the time of IGR application could be related to a temperature sum, the relation between emergence curves of last-instar larvae and temperature sum was studied for several years. For this purpose simulated curves were used, because field-observations on emergence of last-instar larvae covered only two years. Using the established relation between temperature sum and developmental stage of the leafroller population, only temperature sums need to be calculated for the timing of applications of IGR's.

    The isolating effect of greenhouses on arthropod pests [and its significance for integrated pest management] : a case-study on Clepsis spectrana (Lepidoptera: Tortricidae)
    Bos, J. van den - \ 1983
    Landbouwhogeschool Wageningen. Promotor(en): J. de Wilde, co-promotor(en): G.W. Ankersmit. - Wageningen : van den Bos - ISBN 9789022008393 - 93
    tortricidae - insecten - plantenplagen - gewasbescherming - biologische bestrijding - adaptatie - acclimatisatie - milieu - seizoenen - fotoperiode - fotoperiodiciteit - nuttige insecten - clepsis spectrana - microlepidoptera - schadelijke dieren - tortricidae - insects - plant pests - plant protection - biological control - adaptation - acclimatization - environment - seasons - photoperiod - photoperiodism - beneficial insects - clepsis spectrana - microlepidoptera - noxious animals
    Chapter 1: the environmental conditions in greenhouses differ in many respects from those in the open field. Both the climate and the crops are different. A free exchange between the fauna of the greenhouses and the open air is hampered by the glass walls and roofs. The isolating effect of greenhouses on arthropod pests contributes to the effectiveness of control measures, but also to the development and maintenance of pesticide resistance in greenhouses. Because of the special conditions a specific fauna exists in greenhouses, and the use of exotic predators and parasites for biological control is possible. The greenhouse environment acts as a "sieve" only allowing such species to thrive that are adapted to these special conditions. These are sometimes exotic species that cannot thrive in the open in the Dutch climate. Native species may penetrate into greenhouse cultures, but to pass the "sieve" they have to adapt to greenhouse conditions.

    The leaf-roller Clepsis spectrana Tr. is native in the Netherlands. It gives an example of the development of a greenhouse-adapted biotype. In Dutch greenhouses, especially on roses, it causes much damage. In heated greenhouses, where artificial illumination is not given, growth and reproduction of C. spectrana continue without diapause during winter, which is advantageous for the species in this environment, where the difference between summer and winter temperatures does not exceed a few degrees and suitable food is available all the year round.

    Chapter 2 deals with the morphology, bionomics, host plant range, and distribution area of C. spectrana. Chapter 3 describes the materials and methods.

    Chapter 4: the number of larval instars from egg hatching to pupation varied between 4 and 8 in both field and greenhouse strains. Each larval growth type had its own specific progression of head capsule width. The difference in head capsule width between the 4- and 5-instar type was already evident in the 1st instar, between the Sand 6-instar type in the 2nd instar, and between the 6- and 7-instar type only in the 3rd instar or even later. Females tended to develop through a higher number of instars than males, but 5 instars was the most usual in both sexes. The development duration was the same in field and greenhouse strains, in each of the immature stages. The upper thermal limit for development was between 30 °C and 35 °C in both field and greenhouse strains, whereas the developmental threshold was close to 10 °C. An adaptation of greenhouse populations of C. spectrana to development at higher temperatures did not appear.

    Chapter 5: short daylength induced diapause in field strains in the larval stage. The critical photoperiod was between 16 and 17 hours. The number of moults up to the onset of diapause varied between 2 and 6, and was determined by the photoperiod. Larvae from eggs hatching later in the season entered diapause after a lower number of moults. The time of resumption of growth after diapause termination in spring was not correlated with the date of egg hatching in the previous year, in outdoor experiments. The larvae underwent supernumerary moults after termination of diapause. The duration of post-diapause development was longer as diapause had been entered after less moults. The number of moults after termination of diapause, and the duration of post-diapause development, were sex-linked. The functional significance of these phenomena is discussed.

    Chapter 6: the photoperiodic response of 5 different greenhouse strains, originating from larvae and pupae collected in different rose houses at different times of the year (both in summer and in winter), was tested in the laboratory. These greenhouse strains did not enter diapause, at both 20 °C and 15 °C, regardless of the photoperiod, One greenhouse strain was also reared outdoors. Egg hatching dates were August 1, August 17, September 25, and October 14. At least the major part of the larvae did not enter diapause.

    Chapter 7: field strain larvae entered diapause in a heated greenhouse, but the absence of a period of chilling caused an abnormal growth pattern in these larvae, compared to larvae terminating their diapause outdoors: (a) larval development duration was extremely variable (larvae from field strain eggs that hatched at August 24 in the greenhouse, pupated between January 28 and July 15 of the following year), (b) The difference in mean developmental time between male and female larvae was greatly increased, and (c) the mean number of moults, and the variation in the number of moults, Were increased. The survival of diapausing larvae, however, was not essentially affected by the absence of a period of chilling. The time required for diapausing larvae to reach the pupal stage under conditions without a cold period, was genetically determined, and could be shortened rapidly by selection.

    Chapter 8: a difference in the composition of the female sex pheromone between field and greenhouse strains could not be shown, nor in the calling behaviour of virgin females in relation to the light-dark cycle. Release-recapture trials revealed that females of both strains attracted males of both strains in equal proportions. There did not appear to be a difference in mating preference.

    Chapter 9: the index of genetic identity (I) of a field population on stinging nettles from the middle of the country, and a rose house population from the West of the country, amounted to 0.994 (based on allozyme frequencies). This is the level for panmictic populations of one species. Field and greenhouse strains could readily be intercrossed, with a viable F2 generation.

    Chapter 10: field and greenhouse populations of C. spectrana are certainly still conspecific. It is adequate to speak of a "field biotype" and a "greenhouse biotype". The greenhouse biotype is characterised by absence of the ability to enter diapause. When the biotypes are brought together, hybridization and introgression certainly will occur. Immigration of the field biotype into heated greenhouses apparently is sufficiently low to maintain a separate greenhouse biotype with constant characteristics. The origin of the greenhouse biotype might be a non-diapausing geographic race of C. Spectrana, from the warmest parts of its distribution area, or the field biotype immigrated into heated greenhouses, and subsequently lost its ability to enter diapause. The last possibility seems the most likely.

    Chapter 11: pheromonal trapping of C. spectrana is less effective in greenhouses than in the open air. Probably the specific nature of the air movements in greenhouses reduces the effectiveness of the long- range pheromone-mediated behaviour of the males. However, male pheromone-mediated behaviour in short-range orientation, close to calling females, may be unaffected (chapter 8.3). This decreases the effect of synthetic pheromone used for monitoring and mass trapping. However, application of the communication disruption technique may be successful under glass, because the overall concentration of synthetic pheromone in the air can be made much higher in greenhouses than in the open field. Further research is recommended.

    Controlling C. spectrana in greenhouses by releasing sterile males seems feasible, as: (a) immigration of new adults from outside almost certainly is negligible, and (b) C.spectrana is the only tortricid occurring in the Dutch floriculture; the danger that other leaf-rollers will take over when chemical control of C. spectrana ceases seems therefore small.

    Diapause can be crossed into greenhouse populations of C. spectrana by releasing males of the field biotype. This probably is an ineffective way of controlling these populations.

    Parasitised C. spectrana larvae were found in several greenhouses, even in winter. The parasites, which were not identified, apparently were not diapausing. It is recommended to make a survey of the parasite fauna of C. spectrana in greenhouse cultures.

    Bladrollers in appel- en pereboomgaarden
    Jong, D.J. de; Beeke, H. - \ 1982
    Wilhelminadorp : Proefstation voor de Fruitteelt (Mededeling / Proefstation voor de Fruitteelt no. 19) - 218
    insecten - insectenplagen - appels - peren - tortricidae - microlepidoptera - insects - insect pests - apples - pears - tortricidae - microlepidoptera
    Comparative aspects of taste receptors and host plant selection in larvae of various Yponomeuta species (Lepidoptera)
    Drongelen, W. van - \ 1980
    Landbouwhogeschool Wageningen. Promotor(en): L.M. Schoonhoven, co-promotor(en): W.M. Herrebout. - Wageningen : Drongelen - 76
    smaak - smaakgevoeligheid - yponomeuta - gastheerpreferenties - microlepidoptera - yponomeuta - host preferences - taste - taste sensitivity - microlepidoptera

    Caterpillars perceive their food's taste by a limited number of receptor cells. As is shown in several studies reported in literature, gustation plays a crucial rôle in both qualitative and quantitative aspects of feeding responses. In this thesis, a comparative investigation on gustatory perception of plant constituents in several Yponomeuta species is described.

    The species studied, their associated hosts and stimuli applied are shown in Table 1 of the first chapter. Electrophysiological data were obtained by means of a tip recording technique. The sensory cells respond to stimulation by generating a train of action potentials (Fig. 1, chapter 1). A model which can explain the shape and magnitude of the recorded action potentials is described in chapter 6. Routinely the number of spikes during an arbitrary interval of stimulation served as response index. In addition some of the activities were analysed in greater detail. This type of analysis, taking into account the number of activities in each recording and their time courses is described in chapters 1 and 5. Several types of interspecific sensitivity spectra have been recorded and are represented in Table 2 and Fig. 6 in chapter 1. A classification of a complete array of responses was carried out by a cluster analysis and is described in the second chapter; it appears that most species can be distinguished on the basis of functional criteria (Fig. 1, chapter 2). As far as can be determined natural concentrations (Table 1, chapter 1) appear to be situated above receptor cell threshold levels (Fig. 6, chapter 1). General aspect on relationships between receptor cell sensitivity, natural concentrations and data processing by the central nervous system are described in chapter 7. Although the vertebrate olfactory system is used to illustrate the examples in the seventh chapter, the principles described are also valid for the insect gustatory system. In larvae of Y. cagnagellus and Y. evonymellus behavioural responses to some of the stimuli used in the electrophysiological experiments were determined (chapter 3). To study inheritance of gustatory sensitivity, F1 offspring of reciprocal crosses between Y.cagnagellus and Y. malinellus was tested for sensitivity to solutions of dulcitol, phloridzin, prunasin and sorbitol (chapter 4).

    Maatregelen ter preventie van Adoxophyes orana (F.v.R.) plagen
    Anonymous, - \ 1979
    Wageningen : Pudoc (Literatuurlijst / Centrum voor landbouwpublikaties en landbouwdocumentatie no. 4221)
    appels - bibliografieën - vruchtbomen - insecten - malus - boomgaarden - plantenplagen - tortricidae - microlepidoptera - apples - bibliographies - fruit trees - insects - malus - orchards - plant pests - tortricidae - microlepidoptera
    Characterization of nuclear polyhedrosis viruses obtained from Adoxophyes orana and from Barathra brassicae
    Jurkovicova, M. - \ 1979
    Landbouwhogeschool Wageningen. Promotor(en): J.P.H. van der Want, co-promotor(en): D. Peters. - Wageningen : Jurkovicova - 133
    baculovirus - biologische bestrijding - organismen ingezet bij biologische bestrijding - insecten - lepidoptera - noctuidae - kernpolyedervirussen - plantenplagen - tortricidae - virusmorfologie - virologie - virussen - adoxophyes orana - mamestra brassicae - microlepidoptera - baculovirus - biological control - biological control agents - insects - lepidoptera - noctuidae - nuclear polyhedrosis viruses - plant pests - tortricidae - viral morphology - virology - viruses - adoxophyes orana - mamestra brassicae - microlepidoptera
    ln infectivity experiments some A. orana larvae died after being inoculated with an inoculum containing NW isolated from B. brassicae. The polyhedra formed upon infection occluded single virus particles, whereas the inoculum contained polyhedra with bundles of virus particles. This change could be explained either by activation of a virus in A. orana, which is singly embedded, or the inoculum from B. brassicae had infected A. orana and consequently the inclusion of virus particles in outer membranes is controlled by the hosts. This thesis describes studies performed to discriminate between both possibilities. Therefore, the first task was to characterize the virus particles from B. brassicae and A. orana NPV and their polyhedra by different techniques (Chapter 1).

    The properties of the NW of A. orana and of B. brassicae as observed with the electron microscope and polyacrylamide gel electrophoresis are similar to those found for many other NPVs. The polyhedra of both NPVs differ in size and shape. Most of the A. orana polyhedra are globular and range in diameter from 1-2 μm. Most of the B. brassicae polyhedra are hexagonal or pentagonal in outline and range in diameter from 1.5-4 μm. Analysis of polyhedral protein by polyacrylamide gel electrophoresis shows the presence of two polypeptides of molecular weight 28,000 and 54,000 Daltons.

    Treatment of the polyhedra of both viruses with sodium carbonate ruptures the polyhedral membrane and the virus particles and polyhedral proteins are released. The virus particles of A. orana polyhedra are singly embedded in the polyhedral matrix and have a size of 250 x 60 nm. The multiply embedded virus particles of B. brassicae have a size of 347 x 113 nm. Analysis of the viral proteins by SDS-polyacrylamide gel electrophoresis showed that NW of A. orana has 5 polypeptides of 68,000, 48,000, 39,000, 32-34,000, and 28,000 Daltons, respectively. Those of the NPV of B. brassicae were 69,000, 57,000, 46,000, 34-39,000, and 28,000 Daltons, respectively.

    In the polyhedral membrane fractions of both polyhedra one polypeptide of molecular weight of 28,000 Daltons as estimated by polyacrylamide gel electrophoresis, was found.

    Due to proteolytic activity associated with the polyhedra, which is evident after dissociation of the polyhedra, it was difficult to establish the number of polyhedral proteins and their molecular weight (Chapter 2). The electrophoretic pattern of polyhedral proteins of A.orana and B. brassicae polyhedra dissociated in alkali differed from those proteins obtained by other means. Six to seven polypeptides with molecular weights between 28,000 and 8,000 Daltons were found after incubation at pH 10.5. After inactivation of the enzyme only two polypeptides with molecular weights of 28,000 and 26,000 Daltons were observed. When the polyhedral proteins were analysed without incubation at pH 10.5 also two proteins were found, but their molecular weight was 54,000 and 28,000 Daltons.

    On the basis of the results described in Chapters 1 and 2 it can be concluded that the virus particles of B. brassicae and A.orana NPV differ with respect to size, the way of occlusion, and the form and size of the polyhedra involved. Protein analysis by polyacrylamide gel electrophoresis reveal some difference in molecular weight of viral protein but no significant difference in the protein composition of their polyhedra. Further analyses of amino acid composition and sequence of these proteins is necessary to elucidate possible differences.

    To differentiate further between both viruses their genomes were analysed (Chapter 3). Both genomes are circular double-stranded DNA molecules. The molecular weights of A.orana and of B. brassicae NPV-DNAs are 6.7 x 10 7and 8.9 x 10 7Daltons, respectively as determined by electron microscopy and by renaturation kinetic analysis. The renaturation also indicated that both genomes contain only unique sequences. The buoyant density in CsCl of the NPV-DNA of A. orana and of B. brassicae is 1.694 and 1.696 g/cm 3, respectively. These values are in good agreement with (G+C) contents of 34.5 and 37%, respectively as determined by thermal denaturation. The digestion of the A. orana and of the B. brassicae NPV-DNA with endonuclease Eco RI resulted in completely different electrophoretic patterns. Also in experiments on
    competition hybridization no homology between these genomes was found. The conclusion of these studies is that these two NPVs can be clearly differen tiated by their DNA properties.

    In order to study the occurrence of viral DNA in uninfected larvae the DNA of A. orana and B. brassicae was isolated and the complexity studied (Chapter 4). The genomes of A.orana and of B. brassicae differ in their kinetic complexity as estimated from the reassociation data on hyperchromicity, but they are both relatively small and show remarkable similarity in the extent of intragenome homology. A haploid cell of A. orana has a DNA equivalent of 4.2 x 10 10and that of B. brassicae of 8.4 x 10 10Daltons. The intragenome homology was estimated to be 10 and 9% for A.orana and B. brassicae genome, respectively. The (G+C) content, estimated by thermal denaturation, was found to be 36.2% for the A. orana genome and 35.8% for the B. brassicae genome.

    The results obtained during rearing of insects from surface-sterilized eggs and from untreated eggs showed that the NPV of A.orana and of B. brassicae can be transmitted to the progeny of these insects on the outside of the eggs (transovum) as well as inside the eggs (transovarially) (Chapter 5). Evidence for transovarial transmission was also obtained from reassociation of viral DNA with the host DNA of homologous insects reared from surface-sterilized eggs. These experiments revealed the presence of viral sequences in host DNA: 0.03 and about 2.5 viral copies for the diploid quantity of the A. orana and of the B. brassicae host DNA, respectively.

    Results obtained in infectivity experiments with insects in various developmental stages showed that transstadial transmission is a prerequisite for generation-to-generation transmission.

    The presence of a latent virus infection in both insects could also be demonstrated in cross-inoculation experiments (Chapter 6). When the larvae of A. orana and of B. brassicae were inoculated with polyhedra of the reciprocal species, the number of larvae containing polyhedra increased compared with that of the control. Comparison of the restriction endonuclease Eco RI pattern of DNA isolated from polyhedra used as inocula with that from polyhedra obtained after cross-inoculation indicated that both viruses are not cross-infective but that they activate a latent virus infection in both insects. Because the cross- inoculation experiments were done under laboratory conditions (as aseptic as possible), it could be concluded that the B. brassicae NPV is not suitable for biological control of A. orana in the field, because this virus is not cross-infective.

    Ecological and physiological aspects of aestivation-diapause in the larvae of two Pyralid stalk borers of maize in Kenya
    Scheltes, P. - \ 1978
    Landbouwhogeschool Wageningen. Promotor(en): J. de Wilde. - Wageningen : [s.n.] - 110
    insecten - plantenplagen - Zea mays - maïs - Tortricidae - diapauze - hibernatie - aestivatie - groei - Kenya - Pyralidae - microlepidoptera - insects - plant pests - Zea mays - maize - Tortricidae - diapause - hibernation - aestivation - growth - Kenya - Pyralidae - microlepidoptera
    Stalk borers are highly destructive to a large number of important graminaceous crops all over the world. Some examples of economically important stalk borers and a general description of their life-cycle are mentioned in chapter 1. In the same chapter difficulties in controlling the insects are described. The crucial role of aestivation- diapause in the life history of tropical stalk borers is elucidated and the importance of further research on this subject is demonstrated.

    Aestivation-diapause in two Pyralid stalk borers, Chilopartellus (Swinhoe) and Chilo orichalcociliella (Strand) was investigated under field and laboratory conditions.

    The relation between diapause and climate during three consecutive years is described in chapter 2. Yearly and seasonal fluctuations in the larval and pupal populations of the two stalk borers in maize appeared to be considerable. As long as the water conditions for plant growth were suitable, insects had a continuous development. Under these conditions larvae had pigmented spots and could not survive dry conditions. Soon after cessation of the rains (or irrigation) rates of pupation decreased. At that time larvae lost their cuticular pigmentation and became resistant to drought. Comparison of the incidence of aestivation in the field with the prevailing climatic conditions showed that only lack of rain could be associated with the arrested larval development. No effects of temperature, relative humidity or photoperiod could be found. These results indicate that the host plant may be involved in the induction of diapause.

    Chapter 3 is concerned with characteristics of pre-diapause and diapause larvae. Evidence was obtained that under natural conditions larvae do not feed during diapause as long as they are not disturbed. The physiological condition of field-collected stem borer larvae changed considerably upon entering diapause: a decreased rate of oxygen consumption, rate of heart beat and water content, an increased fat content, and arrested development of the testes were found. These changes normally occurred before larvae were turning unspotted and/or were becoming resistant to drought.

    The condition of the host plant in relation to diapause induction is described in chapter 4. Diapause could be induced inside maize plants of different developmental stages. It was shown that the first (physiological) signs of the diapause syndrome appear in larvae feeding in stems containing 70-80% water and very little (< 1.3% of the fresh wt.) protein. The considerable variation in the sugar content of stems containing pre-diapause larvae suggests that sugar is not important in the induction of diapause.

    Marked differences were found in the consumption and utilization of stems of maize plants in different developmental stages. Its possible relevance to diapause is discussed.

    In chapter 5 experiments are described on the induction of aestivation-diapause by varying the food condition. Most early 5th instar larvae of C. partellus entered diapause after being introduced into aged maize stems containing 75% water, 8% sugar and 1.3% protein (fresh wt.). Pupation rate, cuticular pigmentation, QO 2 and water content of these larvae were
    comparable to values obtained from field-collected aestivating larvae. Larvae which had developed beyond the early 5th instar were less sensitive to the diapause inducing factors of the aged maize stem : most of them pupated.

    Test of 30 different diets with varying protein, sugar and water contents, indicated that diets containing 0.9-1.1% protein and 70% water were best in inducing diapause. Early 5th instar larvae on diets with the above mentioned protein content grew slowly (but reached normal weights), moulted into the unspotted form and had a retarded rate of pupation. Larvae on diets with lower protein contents hardly developed at all, whereas on diets with higher protein contents larvae pupated normally. Larvae reared on diets in which the water content had been reduced from the normal level of 86% to 70%, resulted in a
    reduction of the larval water content and respiratory rate, close to values normal for field-collected diapause larvae. Evidence was obtained that larvae reared on diapause inducing diets attained a certain degree of drought resistance. Early 5th instar or younger larvae were the most sensitive stages to diapause induction by diet.

    Many larvae on aged maize stems and artificial diets turned unspotted even though pupating soon thereafter. The relevance of the cuticular pigmentation as a criterion for aestivation-diapause is discussed.

    The endocrine involvement in the aestivation- diapause is described in chapter 6. From juvenile hormone titre determinations and ligation experiments evidence was obtained that the diapause is regulated by an intermediate level of JH. Application of JH to non-diapause larvae prevented pupation of these larvae but did not evoke other aspects of the diapause syndrome.

    Platyptilia gonodactyla en andere soorten Platyptilia
    Anonymous, - \ 1977
    Wageningen : Pudoc (Literatuurlijst / Centrum voor landbouwpublikaties en landbouwdocumentatie no. 4058)
    bibliografieën - insecten - plantenplagen - tortricidae - microlepidoptera - bibliographies - insects - plant pests - tortricidae - microlepidoptera
    Simulation of the fluctuations of the grey larch bud moth
    Bos, J. van den; Rabbinge, R. - \ 1976
    Wageningen : Pudoc (Simulation monographs ) - ISBN 9789022005897
    tortricidae - populatiedynamica - bosbouw - bomen - dieren - populatiedichtheid - populatie-ecologie - mortaliteit - populatiegroei - computersimulatie - simulatie - simulatiemodellen - zwitserland - bosschade - insecten - insectenplagen - larix decidua - microlepidoptera - tortricidae - population dynamics - forestry - trees - animals - population density - population ecology - mortality - population growth - computer simulation - simulation - simulation models - switzerland - forest damage - insects - insect pests - larix decidua - microlepidoptera
    Contributions to an integrated control programme of Hypsipyla grandella (Zeller) in Costa Rica
    Grijpma, P. - \ 1974
    Landbouwhogeschool Wageningen. Promotor(en): J. de Wilde, co-promotor(en): L.M. Schoonhoven. - Wageningen : [s.n.] - 147
    biogeografie - bestrijdingsmethoden - costa rica - ziektebestrijding - ecologie - bosschade - hydrobiologie - insectenplagen - insecten - geïntegreerde bestrijding - geïntegreerde plagenbestrijding - lepidoptera - plagenbestrijding - plantenziekten - plantenplagen - gewasbescherming - tortricidae - hypsipyla grandella - microlepidoptera - biogeography - control methods - costa rica - disease control - ecology - forest damage - hydrobiology - insect pests - insects - integrated control - integrated pest management - lepidoptera - pest control - plant diseases - plant pests - plant protection - tortricidae - hypsipyla grandella - microlepidoptera
    The shootborer Hypsipylagrandella (Zeller) (Lep., Pyralidae) is the main obstacle to the artificial regeneration of valuable meliaceous tree species such as mahogany ( Swietenia spp.) and Spanish cedar ( Cedrela spp.) in Latin America. On the other hand, the natural regeneration of these species is endangered due to depletion of the naturally existing resources and burning in colonization projects.

    This dissertation concerns the development of several fields of research, which when incorporated in a programme of integrated control may contribute to a solution of the Hypsipyla problem.

    Chapter 1 contains a general introduction on this insect pest and its host plants in Costa Rica. In addition, a review is provided of the economic importance of the pest in tropical forestry and of the previous and contemporary investigations on the possibilities of its control.

    The research carried out in the framework of the Inter-American Working Group on Hypsipyla at the tropical Research and Training Centre of the Inter-American Institute of Agricultural Sciences at Turrialba, Costa Rica, is dealt with in Chapter 2.

    These investigations refer to the natural resistance of Meliaceae, host selection, development of an artificial rearing technique for H . grandella and to a survey of parasites in Costa Rica which might be employed in a biological control of the shootborer.

    The main results are:

    a. Two exotic Meliaceae, African mahogany ( Khayaivorensis ) and the Australian cedar ( Toonaciliatavaraustralis ) were introduced and were found to be immune against attacks of the shootborer. Biological and chemical screening for the basis of resistance of the Australian cedar led to the location of two toxic components in the aqueous fraction of young leaves and shoots of this tree species. The toxicity of Toona can be translocated to Cedrelaodorata grafted on the Australian cedar.

    b. Experiments on the host selection of H . grandella point at the existence of a host selection mechanism in which the female adult orients itself towards the host by means of olfaction. Fourth instar larvae of the borer prefer native hosts to exotic species as food sources.

    c. An artificial rearing technique was developed for H . grandella . A diet (Vanderzant) used for rearing Heliothiszea appeared to be a suitable medium for mass rearing Hypsipyla . Although initially mating of adults could only be obtained in outdoor cages in Costa Rica, subsequent rearing in Wageningen, under completely artificial conditions, proved to be perfectly feasible. Larval and pupal periods of H . grandella reared on artificial and natural diets were determined, and compared. Female adults are generally larger than males and live longer. Artificially reared females still restrict oviposition to meliaceous host plants.

    d. A survey of biological control agents of -the shootborer resulted in the following new records of H . grandella parasites in Costa Rica: Trichogramma f asciatum , T . pretiosum , T . near pretiosum , T . semifumatum , Hypomicrogasterhypsipylae sp. n., Brachymeriaconica and Braconchontalensis ; an Agathis sp. has to be identified yet. In addition the nematode Hexamermisalbicans was found to parasitize larvae of the shootborer in Swieteniamacrophylla and Cedrela spp. The egg parasite Trichogrammasemifumatum could be reared easily on eggs of H . grandella .

    Relations between two rice borers in Surinam, Rupela albinella (Cr.) and Diatraea saccharalis (F.), and their hymenopterous larval parasites
    Hummelen, P.J. - \ 1974
    Landbouwhogeschool Wageningen. Promotor(en): J. de Wilde. - Wageningen : Veenman - 89
    insecten - plantenplagen - rijst - oryza sativa - biologische bestrijding - nuttige insecten - tortricidae - parasitoïden - hymenoptera - parasieten - lepidoptera - dierfysiologie - virologie - moleculaire biologie - gewasbescherming - ecologie - diergedrag - gewoonten - microbiologie - microlepidoptera - suriname - insects - plant pests - rice - oryza sativa - biological control - beneficial insects - tortricidae - parasitoids - hymenoptera - parasites - lepidoptera - animal physiology - virology - molecular biology - plant protection - ecology - animal behaviour - habits - microbiology - microlepidoptera - suriname

    In many tropical countries, lepidopterous stem borers are major pests of the rice crop. Study of the rice borers in Surinam, Rupela albinella and Diatraea saccharalis, was made in the Paramaribo area, at the experimental station 'CELOS' during 1971, 1972 and 1973, since data on the ecology and economic importance of these borers were incomplete and almost lacking for the small holders rice areas. Special attention was paid to the role of the parasites of these borers.

    I. R. albinella

    This 'white rice borer' deposits its scale-covered egg masses on the leaves. Newly hatched larvae disperse in a very active way both on plants and on the water surface and they may also use the flow of water. They bore into the stem cavity within 24 hours after hatching. Development to maturity takes place inside one internode. There are five larval instars and only the last two can not be separated by head capsule width. The full-grown larva cuts an exit opening in the stem wall for escape of the adult. The duration of the different developmental stages was determined.

    Normally the percentage of larvae which entered diapause proved to be very low. It was not clear which factor was reponsible for diapause induction. A correlation with a slightly higher temperature (about 2°C) was detected but the data are still too limited to accept the temperature as a basic factor.

    Moths are active during darkness and are attracted by ordinary incandescent light, but are seldom captured during the period of full moon.

    Since Rupela requires an adequate stem cavity for its development, rice plants become vulnerable to attack only 60 days after sowing when a proper internodal space may be present. Rice varieties having a total growth period of only 105 days automatically possess an 'escape resistance', because the larval and pupal development takes about 50 days.

    Generally R. albinella is well adapted to the rice plant. Crop losses are very small since the stem tissue is only attacked superficially.

    Four parasites of R. albinella were found, viz.:

    1. Telenomus sp., an egg parasite with a short life cycle. This insect was not further studied.

    2. Venturia ovivenans, an egg-larval parasite with a high reproduction capacity, parasitizes the eggs. The growth of the parasite larva is moderate until the host is full-grown. Rapid growth follows and the larva leaves its host and pupates inside the stem.
    Development of host and parasite are well sychronized, both in nondiapause and diapause situations. The average time of emergence of the wasp is two days earlier than of the moth.
    The species is very common throughout Surinam.

    3. Strabotes rupelae, a larval and pupal parasite, deposits its eggs near the fullgrown host larva or pupa. The wasp even crawls into the water in search for hosts. The ectoparasitic larva grows very rapidly and sucks out its host. The duration of the life cycle is one third that of the host. The adult life span may be as long as two months.
    The parasite was quite common at the 'CELOS' research centre with its continuous rice cultivation program.

    4. Heterospilus sp., a gregarious and ectoparasitic wasp, lays its eggs in the stem cavity near a full-grown host larva. Larval growth is very rapid and the total life cycle is one third of that of its host.
    The parasite was common at the 'CELOS' research centre.
    The interactions between R. albinella and its parasites are schematically given in Figure 15.

    The greatest mortality occurs in the L 1 during dispersal and penetration of the host plant. Later on, the effect of parasites as well as pupal mortality are important.

    The succession of the generations of the borer and its parasites under the 'CELOS' continuous rice cultivation system is given in Figure 18. Over a period of slightly more than two years, borer infestation slowly increased whereas parasitization of the borer slowly decreased. The percentage composition of the parasitic complex remained stable in these two years.

    II. D. saccharalis

    An existing aseptical diet for the 'brown borer' was improved and made it possible to rear large numbers of borers. The following good rearing results were obtained: total developmental time (35-38 days), pupal weights (males 75 mg, females 125 mg) and egg production (400 eggs/female). A clear correlation was found between pupal weight and egg production.

    It was not possible to accurately separate the 6 larval instars by means of head capsule width. The behaviour of the larvae was followed. Moths emerged before midnight and sometimes copulated the same night. A male copulates once a night and at most, three successive nights. Copulation always occurs late in the night. The first eggs are laid the night after mating.

    Larval and pupal mortality was very high under field circumstances.

    Agathis stigmaterus was the only important parasite. It was reared in large quantities in host larvae feeding on the diet mentioned above. The wasp deposits its eggs in 6-14 day-old hosts. An average of 100 hosts were parasitized per wasp. The parasite first grows slowly; it then leaves the nearly full-grown host and sucks it out within a few hours. There is a good synchronization between the host and the parasite. Only 2 % of the wasps were males.

    Ant nests were present in about 15 % of the rice hills. These ants, Paratrechina sp., feed on the young borer larvae.

    Although D.saccharalis incidentally may cause some local losses, the overall damage is negligible.

    Studies on dispersal of Adoxophyes orana F.v.R. in relation to the population sterilization technique
    Barel, C.J.A. - \ 1973
    Landbouwhogeschool Wageningen. Promotor(en): J. de Wilde. - Wageningen : Veenman - 107
    insecten - plantenplagen - vruchtbomen - boomgaarden - tortricidae - sterilisatie - steriele insecten techniek - genetische gewasbescherming - dieren - territorium - habitats - milieu - plantenziekten - epidemiologie - distributie - adoxophyes orana - microlepidoptera - insects - plant pests - fruit trees - orchards - tortricidae - sterilization - sterile insect release - genetic control - animals - territory - habitats - environment - plant diseases - epidemiology - distribution - adoxophyes orana - microlepidoptera

    In apple growing areas, in the Netherlands, Panonychus ulmi Koch and Adoxophyes orana FvR. are the most important pests. Preliminary experiments had shown that P. ulmi could be controlled by predators, but these predators are killed by insecticide sprayings against other pests.

    As A. orana had already been cultured on an artificial medium, the application of the population sterilization technique was within the realms of possibility. However, the high population density of the species was a disadventage. But if this was counterbalanced by a poor capacity for dispersal, the application of this technique, on a small scale, would be possible. In a simulation model, it was demonstrated that only 100 immigrants per generation per ha, was already too high to make the technique feasible.

    Three modes of dispersal could be expected: flight, aerial transport of larvae with wind and transport of larvae together with plants and packaging materials. The last possibility was not investigated, it was assumed that it could be reduced to a great extent by appropriate measures.

    Dispersal by flight was studied in release-recapture experiments. The released moths were cultured on a meridic diet. For marking, either 32P or the dye Calco oil red D was added to the medium. In order to recapture the moths, light traps and sex traps were used. The experiments were carried out in several places, an open field, orchards, and hedgerows. The results obtained indicated that the movement from the release points was small. The greatest distance at which a male was recaptured in these experiments was 250 m. Only in the experiment in which 75500 males were released homogeneously throughout an orchard of 1.5 ha, were the distances, at which males were still recovered, somewhat greater, but the maximum distance was 435 m. For this particular experiment it was calculated that about 1 to 2 percent of the males had left the orchard. It is assumed that, for this kind of biotope, this a representative percentage.

    In light traps, in general, the numbers of males captured were higher than the numbers of females captured. This could be the result of, either a lower flight activity of the females compared to the males, or an eventual difference in the diurnal flight period of males an females. In laboratory experiments, evidence was obtained for both possibilities.

    Concerning larval dispersal by means of wind, only qualitative data were obtained. It was demonstrated that it occurs frequently and that characteristic behaviour elements are involved. The larva spins a silken thread when it drops off from a leaf. This thread can be broken by the force of the wind, exerted on the thread. It subsequently breaks near the end at which it is attached to the leaf. The buoyancy of the larva in the air depends on the length of the thread. It was demonstrated that wind velocities of more than 3 m per sec have an immobilizing effect on the locomotion of the newly-hatched larvae. It is likely that this behaviour protects the larva against being blown away from the leaf, with a very short thread. Experiments on phototaxis and geotaxis yielded indications that the behaviour of young larvae makes them vulnerable to this mode of dispersal. The behaviour of older larvae was different in this respect. It is likely that, because of the greater weight, the chances for aerial transport of older larvae are reduced. In a qualitative way, aerial transport can be important. At 20 °C and 70 % R.H. the newly-hatched larva can survive 6 hours starvation. With an air speed of 2 m per sec, transport over more than 40 km is possible. The quantative aspects will be determined by the vegetation that surrounds the egg-mass. In an orchard, a large proportion of the larvae will be sieved out from the air, by the surrounding trees.

    A. orana has a wide hostplant range. In preliminary experiments the possibility of a variability of response towards different hostplants was investigated. No indications were found.

    When there is no variability in response towards apple, between A. orana in orchards and A. orana in other biotopes, it is important to know the population densities in these biotopes, especially in the fruit growing areas, where eventually the population sterilization technique is going to be applied. The population densities were estimated in 23 different places, hedgerows, lanes and woods, by releasing a known number of marked moths into the wild population. From the numbers recaptured by means of sex traps, the number of moths of the wild population was calculated, with the aid of the Lincoln-index. The density in woods was found to be lower than the average population density in orchards, but for some hedgerows higher densities were calculated. The calculated densities were highest when a great part of the hedgerows consisted of alder ( Alnus spp.) or hawthorn ( Crateagus sp.).

    The conclusion of these studies was, that with regard to the dispersal of the adults, there is a fair chance that the population sterilization technique can be applied on a small scale, when the area is surrounded by a zone of 500 m, free from other populations of A.orana. If this is not possible, sterilized adults also have to be released in these populations. In this conclusion, the dispersal of larvae by wind, is not taken into consideration. It is assumed that quantitatively, this mode of dispersal is of minor importance.

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