Staff Publications

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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    Artificial light at night causes diapause inhibition and sex-specific life history changes in a moth
    Geffen, K.G. van; Grunsven, R.H.A. van; Ruijven, J. van; Berendse, F. ; Veenendaal, E.M. - \ 2014
    Ecology and Evolution 4 (2014)11. - ISSN 2045-7758 - p. 2082 - 2089.
    epirrita-autumnata lepidoptera - body-size - plutella-xylostella - utetheisa-ornatrix - diamondback moth - lobesia-botrana - flight ability - geometridae - biodiversity - plasticity
    Rapidly increasing levels of light pollution subject nocturnal organisms to major alterations of their habitat, the ecological consequences of which are largely unknown. Moths are well-known to be attracted to light at night, but effects of light on other aspects of moth ecology, such as larval development and life-history, remain unknown. Such effects may have important consequences for fitness and thus for moth population sizes. To study the effects of artificial night lighting on development and life-history of moths, we experimentally subjected Mamestra brassicae (Noctuidae) caterpillars to low intensity green, white, red or no artificial light at night and determined their growth rate, maximum caterpillar mass, age at pupation, pupal mass and pupation duration. We found sex-specific effects of artificial light on caterpillar life-history, with male caterpillars subjected to green and white light reaching a lower maximum mass, pupating earlier and obtaining a lower pupal mass than male caterpillars under red light or in darkness. These effects can have major implications for fitness, but were absent in female caterpillars. Moreover, by the time that the first adult moth from the dark control treatment emerged from its pupa (after 110 days), about 85% of the moths that were under green light and 83% of the moths that were under white light had already emerged. These differences in pupation duration occurred in both sexes and were highly significant, and likely result from diapause inhibition by artificial night lighting. We conclude that low levels of nocturnal illumination can disrupt life-histories in moths and inhibit the initiation of pupal diapause. This may result in reduced fitness and increased mortality. The application of red light, instead of white or green light, might be an appropriate measure to mitigate negative artificial light effects on moth life history.
    Dealing with double trouble: consequences of single and double herbivory in Brassica juncea
    Mathur, V. ; Tytgat, T.O.G. ; Graaf, R.M. de; Kalia, V. ; Reddy, A.S. ; Vet, L.E.M. ; Dam, N.M. van - \ 2013
    Chemoecology 23 (2013)2. - ISSN 0937-7409 - p. 71 - 82.
    induced plant-responses - milkweed asclepias-syriaca - plutella-xylostella - specialist herbivores - induced resistance - diamondback moth - wild radish - nicotiana-attenuata - insect resistance - black mustard
    In their natural environment, plants are often attacked simultaneously by many insect species. The specificity of induced plant responses that is reported after single herbivore attacks may be compromised under double herbivory and this may influence later arriving herbivores. The present study focuses on the dynamics of induced plant responses induced by single and double herbivory, and their effects on successive herbivores. Morphological (leaf length, area and trichome density) and chemical changes (leaf alkenyl and indole glucosinolates) in Brassica juncea were evaluated 4, 10, 14 and 20 days after damage by the specialist Plutella xylostella alone, or together with the generalist Spodoptera litura. To assess the biological effect of the plant's responses, the preference and performance of both herbivores on previously induced plants were measured. We found that alkenyl glucosinolates were induced 20 days after damage by P. xylostella alone, whereas their levels were elevated as early as 4 days after double herbivory. Trichome density was increased in both treatments, but was higher after double herbivory. Interestingly, there was an overall decrease in indole glucosinolates and an increase in leaf size due to damage by P. xylostella, which was not observed during double damage. S. litura preferred and performed better on undamaged plants, whereas P. xylostella preferred damaged plants and performed better on plants damaged 14 and 10 days after single and double herbivory, respectively. Our results suggest that temporal studies involving single versus multiple attacker situations are necessary to comprehend the role of induced plant responses in plant-herbivore interactions.
    Changes in frequencies of genes that enable Phyllotreta nemorum to utilize its host plant, Barbarea vulgaris, vary in magnitude and direction, as much within as between seasons
    Vermeer, K.M.C.A. ; Verbaarschot, P. ; Jong, P.W. de - \ 2012
    Entomologia Experimentalis et Applicata 144 (2012)1. - ISSN 0013-8703 - p. 37 - 44.
    flea beetle - conferring resistance - plutella-xylostella - diamondback moth - ssp arcuata - defenses - identification - coevolution - dynamics - genetics
    The interaction between the flea beetle, Phyllotreta nemorum L. (Coleoptera: Chrysomelidae), and its host plants is well suited to study the dynamics of a geographic mosaic of (co)evolution. The flea beetle can either be resistant or susceptible to the defense of one of its host plants, Barbarea vulgaris R.Br. G-type (Brassicaceae). Previous findings suggested that the frequency of resistant beetles on host plants other than the G-type of B. vulgaris had decreased over time within the period of 1999–2003. In 2008 and 2009 new sampling was performed to investigate whether or not this decrease in frequency of resistance of the flea beetles formed a continuing trend and whether or not the frequency of resistant beetles also varies within the year. The frequency of resistant beetles on different host plants was determined during the reproductive season of the flea beetles in both years. Overall, the frequencies of resistant beetles on B. vulgaris (G-type) remained close to 100%, as found before, but those on other host plants did not consistently decrease across the years, in contrast to what had been suggested. Furthermore, the repeated sampling revealed that the frequency of resistant beetles differed significantly within a season. The present data show that relative frequencies of different resistance phenotypes of P. nemorum on other host plants than B. vulgaris (G-type) are highly dynamic, both within and across years. Therefore, monitoring the changes in these resistance frequencies should involve season-wide sampling efforts. Although the monitoring in this study does not provide an explanation for the observed dynamics, we propose a testable scenario.
    Variation in the specificity of plant volatiles and their use by a specialist and a generalist parasitoid
    Gols, R. ; Veenemans, C. ; Potting, R.P.J. ; Smid, H.M. ; Dicke, M. ; Harvey, J.A. ; Bukovinszky, T. - \ 2012
    Animal Behaviour 83 (2012)5. - ISSN 0003-3472 - p. 1231 - 1242.
    plutella-xylostella lepidoptera - diadegma species hymenoptera - host-selection principle - diamondback moth - headspace volatiles - semiclausum hellen - indirect defenses - natural variation - infochemical use - memory dynamics
    Herbivore-induced plant volatiles (HIPV) provide important information that influences host location behaviour for insect natural enemies, such as parasitoid wasps, that develop in the bodies of herbivorous insects. The dietary breadth of both the parasitoid and its host may affect the extent to which a searching parasitoid relies on HIPV. Specialist species are expected to rely on specific volatile cues to which they respond innately, whereas generalists are expected to show a higher degree of phenotypic plasticity that depends on foraging experience in the parasitoid. We compared the response to HIPV emitted by different plant species damaged by host and nonhost caterpillars for two congeneric parasitoid species, the specialist Diadegma semiclausum and the generalist Diadegma fenestrale, attacking caterpillars of the diamondback moth, Plutella xylostella. For the three tested plant species, Brassica oleracea, a feral Brassica population and Sinapis alba, both parasitoid species preferred volatiles from host-infested plants over those produced by undamaged plants. However, both parasitoid species only distinguished between volatiles induced by host and nonhosts when the caterpillars had been feeding on B. oleracea, the plant on which they had been reared. Chemical analysis of the volatile blends could not explain volatile preferences of the parasitoids. Despite the difference in their dietary breadth, the two parasitoids responded similarly to HIPV and experience treatments. A flexible response to a wide array of volatile blends by parasitoids is probably important in nature, given that different generations of the host and the parasitoid probably develop on different food plants.
    Consequences of constitutive and induced variation in the host's food plant quality for parasitoid larval development
    Bukovinszky, T. ; Gols, R. ; Smid, H.M. ; Bukovinszkine Kiss, G. ; Dicke, M. ; Harvey, J.A. - \ 2012
    Journal of Insect Physiology 58 (2012)3. - ISSN 0022-1910 - p. 367 - 375.
    diadegma species hymenoptera - plutella-xylostella lepidoptera - nutritional ecology - defensive chemistry - copidosoma-sosares - cotesia-congregata - insect parasitoids - diamondback moth - performance - ichneumonidae
    Constitutive and induced changes in plant quality impact higher trophic levels, such as the development of parasitoids, in different ways. An efficient way to study how plant quality affects parasitoids is to examine how the parasitoid larva is integrated within the host during the growth process. In two experiments, we investigated the effects of varying nutritional quality of Brassica oleracea on parasitoid larval development inside the host, the diamondback moth (Plutella xylostella). First, we compared larval growth of the specialist Diadegma semiclausum and the generalist Diadegma fenestrale, when the host was feeding on Brussels sprout plants that were either undamaged or were previously induced by caterpillar damage. Larvae of the generalist D. fenestrale showed lower growth rates than larvae of the specialist D. semiclausum, and this difference was more pronounced on herbivore-induced plants, suggesting differences in host-use efficiency between parasitoid species. The growth of D. semiclausum larvae was also analyzed in relation to herbivore induction on Brussels sprouts and on a wild B. oleracea strain. Parasitoid growth was more depressed on induced than on undamaged control plants, and more on wild cabbage than on Brussels sprouts, which was largely explained by differences in host mass. The effects of induction of wild Brassica on parasitoid development were pronounced early on, but as P. xylostella feeding began inducing the previously undamaged control plants, the effect of induction disappeared, revealing a temporal component of plant-parasitoid interactions. This study demonstrates how insights into the physiological aspects of host-parasitoid interactions can improve our understanding of the effects of plant-related traits on parasitoid wasps.
    Assessing risks and benefits of floral supplements in conservation biological control
    Winkler, K. ; Wackers, F.L. ; Termorshuizen, A.J. ; Lenteren, J.C. van - \ 2010
    BioControl 55 (2010)6. - ISSN 1386-6141 - p. 719 - 727.
    diamondback moth - euphydryas-chalcedona - field conditions - honeydew sugars - nectar sources - lepidoptera - parasitoids - resources - oviposition - herbivores
    The use of flowering field margins is often proposed as a method to support biological control in agro-ecosystems. In addition to beneficial insects, many herbivores depend on floral food as well. The indiscriminate use of flowering species in field margins can therefore lead to higher pest numbers. Based on results from field observations and laboratory experiments we assessed risks as well as benefits associated with the provision of nectar plants in field margins, using Brussels sprouts as a model system. Results show that Brussels sprouts bordered by nectar plants suitable for the cabbage white Pieris rapae L., suffered higher infestation levels by this herbivore. In contrast, nectar plants providing accessible nectar for the diamondback moth Plutella xylostella L., did not raise densities of P. xylostella larvae in the Brassica crop. Margins with Anethum graveolens L., selected on the basis of its suitability as nectar plant for parasitoids, significantly increased the number of adult Diadegma semiclausum Hellen in the crop. This didn't translate into enhanced parasitism rates, as parasitism of P. xylostella by D. semiclausum exceeded 65 % in all treatments, irrespective of the plants in the field margin. Our findings emphasize the importance of taking a multitrophic approach when choosing flowering field margin plants for biocontrol or other ecosystem services
    Insect oviposition behavior affects the evolution of adaptation to Bt crops: consequences for refuge policies
    Jongsma, M.A. ; Gould, F. ; Legros, M. ; Yang, L. ; Loon, J.J.A. van; Dicke, M. - \ 2010
    Evolutionary Ecology 24 (2010)5. - ISSN 0269-7653 - p. 1017 - 1030.
    armigera hubner lepidoptera - helicoverpa-zea lepidoptera - transgenic cotton - diamondback moth - pink-bollworm - resistance - noctuidae - field - suppression - management
    The major lepidopteran insect pests of cotton and maize harbor intra-specific variation for behavior determining the selection of host plants for oviposition. Yet, the consequences of behavioral adaptation for fitness have neither been modeled nor monitored for Bt cotton and maize crops, the most widely grown transgenic herbivore-resistant plants. Here, we present a general two-locus heuristic model to examine potential outcomes of natural selection when pest populations initially have low frequencies of alleles for both physiological and behavioral adaptation to Bt crops. We demonstrate that certain ecological conditions allow for the evolution of behavioral choices favoring alternative oviposition hosts that limit the increase in resistance alleles, even when they are phenotypically dominant. These results have implications for current refuge policies, which should be adapted to promote the evolution of certain behavioral choices for alternative oviposition hosts in addition to dilution of physiological resistance alleles. Collection of data on oviposition host preference as a component of monitoring schemes will provide important insights into mechanisms underlying the durability of Bt-transgenic host-plant resistance
    The effect of host developmental stage at parasitism on sex-related size differentiation in a larval endoparasitoid
    Gols, R. ; Harvey, J.A. - \ 2009
    Ecological Entomology 34 (2009)6. - ISSN 0307-6946 - p. 755 - 762.
    body-size - diadegma-semiclausum - diamondback moth - development time - plant chemistry - dimorphism - hymenoptera - insects - growth - ichneumonidae
    For their larval development, parasitoids depend on the quality and quantity of resources provided by a single host. Therefore, a close relationship is predicted between the size of the host at parasitism and the size of the emerging adult wasp. This relationship is less clear for koinobiont than for idiobiont parasitoids. • As size differentiation in host species exhibiting sexual size dimorphism (SSD) is likely to occur already during larval development, in koinobiont larval endoparasitoids the size of the emerging adult may also be constrained based on the sex of the host caterpillar. • Sex-specific growth trajectories were compared in unparasitised Plutella xylostella caterpillars and in second and fourth instar hosts that were parasitised by the solitary larval koinobiont endoparasitoid Diadegma semiclausum. Both species exhibit SSD, where females are significantly larger than males. • Healthy female P. xylostella caterpillars developed significantly faster than their male conspecifics. Host regulation induced by D. semiclausum parasitism depended on the instar attacked. Parasitism in second-instar caterpillars reduced growth compared to healthy unparasitised caterpillars, whereas parasitism in fourth-instar caterpillars arrested development. The reduction in growth was most pronounced in hosts producing male D. semiclausum. • Parasitism itself had the largest impact on host growth. SSD in the parasitoid is mainly the result of differences in growth rate of the parasitoid-host complex producing male and female wasps and differences in exploitation of the host resources. Female wasps converted host biomass more efficiently into adult biomass than males.
    Lack of correlation between constitutive and induced resistance to a herbivore in crucifer plants: real or flawed by experimental methods?
    Zhang, P.J. ; Shu, J.P. ; Wu, Z.Y. ; Dicke, M. ; Liu, S.S. - \ 2009
    Entomologia Experimentalis et Applicata 131 (2009)1. - ISSN 0013-8703 - p. 58 - 66.
    jasmonate-induced responses - diamondback moth - oviposition preference - arabidopsis-thaliana - volatile emission - indirect defenses - methyl jasmonate - trade-offs - acid - lepidoptera
    The correlation between constitutive and induced resistance to herbivores in plants has long been of interest to evolutionary biologists, and various approaches to determining levels of resistance have been used in this field of research. In this study, we examined the relationship between constitutive and induced resistance to the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), in 11 closely related species of wild crucifers. We assessed the survival, development, and reproduction of the test insects and calculated their intrinsic rate of increase as an indicator of constitutive and induced resistance for the plants. We used larvae of P. xylostella and jasmonic acid as elicitors of the induced response. We failed to find a correlation between constitutive and induced resistance in these crucifer plants when the induction of resistance was initiated by either herbivory or jasmonic acid application. Analysis of the results suggests that the failure to detect a relationship between the two types of resistance could be caused by flaws in measuring constitutive resistance, which was apparently confounded with induced resistance. We discuss the difficulties and pitfalls in measuring constitutive resistance and ways to improve the methodology in investigating the relationships between constitutive and induced resistance in plants
    Performance of specialist and generalist herbivores feeding on cabbage cultivars is not explained by glucosinolate profiles
    Poelman, E.H. ; Galiart, R.J.F.H. ; Raaijmakers, C.E. ; Loon, J.J.A. van; Dam, N.M. van - \ 2008
    Entomologia Experimentalis et Applicata 127 (2008)3. - ISSN 0013-8703 - p. 218 - 228.
    rape brassica-napus - oilseed rape - phytophagous insects - plutella-xylostella - wild populations - diamondback moth - pieris-rapae - resistance - mustard - responses
    Plants display a wide range of chemical defences that may differ in effectiveness against generalist and specialist insect herbivores. Host plant-specific secondary chemicals such as glucosinolates (GS) in Brassicaceae typically reduce the performance of generalist herbivores, whereas specialists have adaptations to detoxify these compounds. The concentration of glucosinolates may also alter upon herbivory, allowing the plant to tailor its response to specifically affect the performance of the attacking herbivore. We studied the performance of three Lepidoptera species, two specialists [Pieris rapae L. (Pieridae), Plutella xylostella L. (Yponomeutidae)] and one generalist [Mamestra brassicae L. (Noctuidae)], when feeding on eight cultivars of Brassica oleracea L. and a native congener (Brassica nigra L.) and related this to the GS content. We tested the hypotheses (i) that a generalist herbivore is more affected by high GS concentrations, and (ii) that generalist feeding has a stronger effect on GS levels. Although performance of the three herbivores was different on the B. oleracea cultivars, M. brassicae and P. xylostella had a similar ranking order of performance on the eight cultivars. In most of the cultivars, the concentration of indole GS was significantly higher after feeding by P. rapae or M. brassicae than after P. xylostella feeding. As a consequence, the total concentration of GS in the cultivars showed a different ranking order for each herbivore species. The generalist M. brassicae performed equally well as the specialist P. xylostella on cultivars with high concentrations of GS. Our findings suggest that secondary metabolites other than GSs or differences in nutrient levels affect performance of the species studied.
    Early season herbivore differentially affects plant defence responses to subsequently colonizing herbivores and their abundance in the field
    Poelman, E.H. ; Broekgaarden, C. ; Loon, J.J.A. van; Dicke, M. - \ 2008
    Molecular Ecology 17 (2008)14. - ISSN 0962-1083 - p. 3352 - 3365.
    tritrophic interaction webs - phytophagous insects - nicotiana-attenuata - induced resistance - diamondback moth - host-plant - interspecific interactions - plutella-xylostella - generalist herbivores - proteinase-inhibitors
    Induction of plant defences by early season herbivores can mediate interspecific herbivore competition. We have investigated plant-mediated competition between three herbivorous insects through studies at different levels of biological integration. We have addressed (i) gene expression; (ii) insect behaviour and performance under laboratory conditions; and (iii) population dynamics under field conditions. We studied the expression of genes encoding a trypsin inhibitor and genes that are involved in glucosinolate biosynthesis in response to early season herbivory by Pieris rapae caterpillars in Brassica oleracea plants. Furthermore, we studied the interaction of these transcriptional responses with responses to secondary herbivory by the two specialist herbivores, P. rapae and Plutella xylostella, and the generalist Mamestra brassicae. P. rapae-induced responses strongly interacted with plant responses to secondary herbivory. Sequential feeding by specialist herbivores resulted in enhanced or similar expression levels of defence-related genes compared to primary herbivory by specialists. Secondary herbivory by the generalist M. brassicae resulted in lower gene expression levels than in response to primary herbivory by this generalist. Larval performance of both specialist and generalist herbivores was negatively affected by P. rapae-induced plant responses. However, in the field the specialist P. xylostella was more abundant on P. rapae-induced plants and preferred these plants over undamaged plants in oviposition experiments. In contrast, the generalist M. brassicae was more abundant on control plants and preferred undamaged plants for oviposition. P. rapae did not discriminate between plants damaged by conspecifics or undamaged plants. Our study shows that early season herbivory differentially affects transcriptional responses involved in plant defence to secondary herbivores and their population development dependent upon their degree of host plant specialization.
    Barbarea vulgaris glucosinolate phenotypes differentially affect performance and preference of two different species of Lepidopteran herbivores
    Leur, H. van; Vet, L.E.M. ; Putten, W.H. van der; Dam, N.M. van - \ 2008
    Journal of Chemical Ecology 34 (2008)2. - ISSN 0098-0331 - p. 121 - 131.
    host-plant selection - p-napi-oleracea - plutella-xylostella - diamondback moth - 2-phenylethyl glucosinolate - oviposition behavior - pieris-rapae - brassicae lepidoptera - arabidopsis-thaliana - feeding deterrent
    The composition of secondary metabolites and the nutritional value of a plant both determine herbivore preference and performance. The genetically determined glucosinolate pattern of Barbarea vulgaris can be dominated by either glucobarbarin (BAR-type) or by gluconasturtiin (NAS-type). Because of the structural differences, these glucosinolates may have different effects on herbivores. We compared the two Barbarea chemotypes with regards to the preference and performance of two lepidopteran herbivores, using Mamestra brassicae as a generalist and Pieris rapae as a specialist. The generalist and specialist herbivores did not prefer either chemotype for oviposition. However, larvae of the generalist M. brassicae preferred to feed and performed best on NAS-type plants. On NAS-type plants, 100% of the M. brassicae larvae survived while growing exponentially, whereas on BAR-type plants, M. brassicae larvae showed little growth and a mortality of 37.5%. In contrast to M. brassicae, the larval preference and performance of the specialist P. rapae was unaffected by plant chemotype. Total levels of glucosinolates, water soluble sugars, and amino acids of B. vulgaris could not explain the poor preference and performance of M. brassicae on BAR-type plants. Our results suggest that difference in glucosinolate chemical structure is responsible for the differential effects of the B. vulgaris chemotypes on the generalist herbivore.
    Temporal changes affect plant chemistry and tritrophic interactions
    Gols, R. ; Raaijmakers, C.E. ; Dam, N.M. van; Dicke, M. ; Bukovinszky, T. ; Harvey, J.A. - \ 2007
    Basic and Applied Ecology 8 (2007)5. - ISSN 1439-1791 - p. 421 - 433.
    glucosinolate content - plutella-xylostella - diamondback moth - seasonal-changes - abiotic factors - trophic levels - pieris-rapae - herbivore - host - lepidoptera
    In nature, individuals of short-lived plant species (e.g. annuals, biennials) may grow at different times during the growing season. These plants are therefore exposed to different season-related conditions such as light and temperature, which in turn may have consequences for primary and secondary chemistry of the plant. Despite this, many studies examining plant¿consumer interactions are performed in single replicates, which may thus ignore temporal variation in the expression of phenotypic plant traits that affect multitrophic interactions. In the present study, we demonstrated that even under strictly controlled conditions in a greenhouse, secondary plant chemistry changes dramatically in plants growing at different times in a single year, i.e. July, August and November. Glucosinolate (GS) contents in herbivore-damaged leaves of two different crucifer species, Brassica oleracea and Sinapis alba were higher in the August and November replicates than in the July replicate and GS concentrations were 10¿25 times higher in S. alba than in B. oleracea. The development of a specialist herbivore, Plutella xylostella, also varied significantly over the three replicates. Larvae of P. xylostella that had fed upon either S. alba or B. oleracea, attained the largest biomass and had the fastest development rate in the November replicate. Female P. xylostella moths grew larger on S. alba than on B. oleracea, whereas male biomass was not significantly affected by host-plant species. Plant species, but not season also affected performance of the endoparasitoid, Diadegma semiclausum. Similar to the performance of host females, parasitoid males developed faster and attained the highest biomass when attacking P. xylostella larvae feeding on S. alba. Most importantly, the performance of the herbivore and its parasitoid only appeared to partially conform to levels of GS in damaged leaves, indicating that there is a complex of factors involved in determining the effects of plant quality on higher trophic levels.
    Sugar resources are vital for Diadegma semiclausum fecundity under field conditions
    Winkler, K. ; Wackers, F. ; Bukovinszkine-Kiss, G. ; Lenteren, J.C. van - \ 2006
    Basic and Applied Ecology 7 (2006)2. - ISSN 1439-1791 - p. 133 - 140.
    parasitoid microplitis-croceipes - hymenoptera-ichneumonidae - habitat management - biological-control - diamondback moth - natural enemies - life-span - lepidoptera - nectar - food
    Many insects, including parasitoids, depend in their adult stage on carbohydrate-rich food as their main source of energy for longevity, fecundity and mobility. The effect of food availability on parasitoid Life table parameters is usually studied in laboratory experiments. However, these studies might be a poor representation of the field situation. Field experiments, on the other hand, are usually unsuitable to evaluate the impact of food availability on individual insects. To bridge this gap, we conducted a field experiment in which individual parasitoid wasps (Diadegma semiclausum) were released in large cages either containing spatially separated food and host (Plutella xylostella) sites, or host sites only (control). Out of the 11 wasps exposed to host larvae in the absence of a nectar source, only three were able to parasitize any larvae. Female wasps that had no access to nectar parasitized only 3.7 +/- 4.4 larvae. In contrast, all 12 wasps with nectar supply were able to parasitize more than 300 P. xylostella, with an average of 390 +/- 31 caterpillars parasitized per wasp. Nectar availability also increased the average reproductive lifespan of the parasitoids from 1.2 days (control) to 28 days. Surprisingly, the impact of food sources on D. semiclausum fecundity was more clear-cut than in previous laboratory studies with the same species, emphasizing the importance of studying life-table parameters under more natural conditions. These results also underline that access to carbohydrate-rich food can be indispensable to parasitoid fecundity and stress the importance of providing suitable nectar sources as an integral part of biological control programs.
    Impact of botanical extracts derived from Melia azedarach and Azadirachta indica on populations of Plutella xylostella and its natural enemies: a field test of laboratory findings
    Charleston, D.S. ; Kfir, R. ; Dicke, M. ; Vet, L.E.M. - \ 2006
    Biological Control 39 (2006)1. - ISSN 1049-9644 - p. 105 - 114.
    diamondback moth - parasitoid populations - cotesia-plutellae - trophic levels - plants - lepidoptera - arthropods - herbivore - volatiles - context
    Differences between results from ecological laboratory studies and what actually happens in the field can be large. Therefore, field experiments are essential to validate laboratory findings. In previous laboratory trials we investigated the impact of aqueous leaf extracts from the syringa tree, Melia azedarach L. (Meliaceae) and commercial formulations from the neem tree, Azadirachta indica Juss. (Meliaceae), Neemix 4.5®, on the biology and behaviour of the diamondback moth Plutella xylostella and two of its most abundant parasitoids, Cotesia plutellae and Diadromus collaris. In the laboratory we had demonstrated that these botanical extracts had adverse effects on survival, fecundity, development, oviposition and feeding of P. xylostella, but no direct negative effects on the survival and foraging of the parasitoids. In the current study, we verified the importance of these previous laboratory findings through field experiments. We treated cabbage plants in the field with the neem product and syringa extract and assessed the infestation levels of P. xylostella and the parasitism rates by natural enemies. Infestation levels of P. xylostella were similar in the plots treated with the botanical extracts and the control plots. However, the damage in the treated plots was significantly lower than in the control plots, indicating that reduced feeding by P. xylostella was a more important factor in the reduction of damage than the actual population density. The proportion of marketable cabbages was significantly higher in the treatments than in the control. The proportion of parasitoids found emerging from P. xylostella was also significantly higher in the treated plots than in the control plots and direct observations indicated that parasitoids still visited cabbage plants that had been treated with the botanical extracts
    AFLP markers for the R-gene in the flea beetle, Phyllotreta nemorum, conferring resistance to defenses in Barbarea vulgaris
    Breuker, C.J. ; Victoir, K. ; Jong, P.W. de; Meijden, E. van der; Brakefield, P.M. ; Vrieling, K. - \ 2005
    Journal of Insect Science 5 (2005). - ISSN 1536-2442 - p. 38 - 38.
    atypical host-plant - plutella-xylostella - diamondback moth - lucilia-cuprina - asymmetry phenotype - diazinon resistance - culex-pipiens - identification - brassicaceae - specificity
    A so-called R-gene renders the yellow-striped flea beetle Phyllotreta nemorum L. (Coleoptera: Chrysomelidae: Alticinae) resistant to the defenses of the yellow rocket Barbarea vulgaris R.Br. (Brassicacea) and enables it to use it as a host plant in Denmark. In this study, genetic markers for an autosomal R-gene, inherited as a single, dominant locus in flea beetles from the Danish locality "Kværkeby" are described, and a genetic linkage map around this particular R-gene is constructed, using the technique of AFLP (Amplified Fragment Length Polymorphism)
    The role of pre- and post- alighting detection mechanisms in the responses to patch size by specialist herbivores
    Bukovinszky, T. ; Potting, R.P.J. ; Clough, Y. ; Lenteren, J.C. van; Vet, L.E.M. - \ 2005
    Oikos 109 (2005)3. - ISSN 0030-1299 - p. 435 - 446.
    moth plutella-xylostella - pieris-rapae - diamondback moth - oviposition behavior - cabbage butterflies - cruciferous plants - population-density - chemical ecology - l lepidoptera - host
    Experimental data on the relationship between plant patch size and population density of herbivores within fields often deviates from predictions of the theory of island biogeography and the resource concentration hypothesis. Here we argue that basic features of foraging behaviour can explain different responses of specialist herbivores to habitat heterogeneity. In a combination of field and simulation studies, we applied basic knowledge on the foraging strategies of three specialist herbivores: the cabbage aphid (Brevicoryne brassicae), the cabbage butterfly (Pieris rapae L.) and the diamondback moth (Plutella xylostella L.), to explain differences in their responses to small scale fragmentation of their habitat. In our field study, populations of the three species responded to different sizes of host plant patches (9 plants and 100 plants) in different ways. Densities of winged cabbage aphids were independent of patch size. Egg-densities of the cabbage butterfly were higher in small than in large patches. Densities of diamondback moth adults were higher in large patches than in small patches. When patches in a background of barley were compared with those in grass, densities of the cabbage aphid and the diamondback moth were reduced, but not cabbage butterfly densities. To explore the role of foraging behaviour of herbivores on their response to patch size, a spatially explicit individual-based simulation framework was used. The sensory abilities of the insects to detect and respond to contact, olfactory or visual cues were varied. Species with a post-alighting host recognition behaviour (cabbage aphid) could only use contact cues from host plants encountered after landing. In contrast, species capable with a pre-alighting recognition behaviour, based on visual (cabbage butterfly) or olfactory (diamondback moth) cues, were able to recognise a preferred host plant whilst in flight. These three searching modalities were studied by varying the in flight detection abilities, the displacement speed and the arrestment response to host plants by individuals. Simulated patch size - density relationships were similar to those observed in the field. The importance of pre- and post- alighting detection in the responses of herbivores to spatial heterogeneity of the habitat is discussed
    Variation in plant volatiles and attraction of the parasitoid Diadegma semiclausum (Hellén)
    Bukovinszky, T. ; Gols, R. ; Posthumus, M.A. ; Vet, L.E.M. ; Lenteren, J.C. van - \ 2005
    Journal of Chemical Ecology 31 (2005)3. - ISSN 0098-0331 - p. 461 - 480.
    enemy-free space - diaeretiella-rapae hymenoptera - brussels-sprouts plants - plutella-xylostella - host-plant - foraging behavior - diamondback moth - natural enemies - cabbage plants - rubecula hymenoptera
    Differences in allelochemistry of plants may influence their ability to attract parasitoids.We studied responses of Diadegma semiclausum (Hellén), a parasitoid of the diamondback moth (Plutella xylostella L.), to inter- and intraspecific variation in odor blends of crucifers and a non-crucifer species. Uninfested Brussels sprout (Brassica oleracea L. gemmifera), white mustard (Sinapis alba L.), a feral Brassica oleracea, and malting barley (Hordeum vulgare L.) were compared for their attractivity to D. semiclausum in a Y-tube bioassay. Odors from all plants were more attractive to the parasitoid than clean air. However, tested against each other, parasitoids preferred the volatile blend from the three cruciferous species over that of malting barley.Wasps also discriminated between uninfested crucifers: mustard was as attractive as feral B. oleracea, and both were more attractive than Brussels sprout. Attractivity of uninfested plants was compared with that of plants infested by larvae of the host P. xylostella. Host-infested mustard and Brussels sprout were more attractive than uninfested conspecifics. Interestingly, the volatile blends of uninfested white mustard and infested Brussels sprout were equally attractive.We also compared the volatile composition of different plant sources by collecting headspace samples and analysing them with GC-MS. Similarities of volatile profiles were determined by hierarchic clustering and non-metric scaling based on the Horn-index. Due to the absence of several compounds in its blend, the volatile profile of barley showed dissimilarities from blends of crucifers. The odor profile of white mustard was distinctly different from the two Brassicaceae.Feral Brassica oleracea odor profile was different from infested Brussels sprout, but showed overlap with uninfested Brussels sprout. Odor blends from infested and uninfested Brussels sprout were similar, and mainly quantitative differences were found. D. semiclausum appears to discriminate based on subtle differences in volatile composition of odor blends from infested and uninfested plants
    Reduced foraging efficiency of a parasitoid under habitat complexity: implications for population stability and species coexistence
    Gols, R. ; Bukovinszky, T. ; Hemerik, L. ; Harvey, J.A. ; Lenteren, J.C. van; Vet, L.E.M. - \ 2005
    Journal of Animal Ecology 74 (2005)6. - ISSN 0021-8790 - p. 1059 - 1068.
    diadegma-semiclausum hellen - enemy-free space - insect parasitoids - natural enemies - searching efficiency - plutella-xylostella - diamondback moth - plant volatiles - trophic levels - herbivore
    1. Habitat complexity may stabilize interactions among species of different trophic levels by providing refuges to organisms of lower trophic levels. 2. Searching behaviour of the parasitoid, Diadegma semiclausum, was followed in different semifield set-ups, a low and high-density monoculture of Brassica oleracea and two intercrops, B. oleracea with Sinapis alba (also a member of the Brassicaceae) and B. oleracea with Hordeum vulgare (Poaceae). 3. When a low-density monocrop of B. oleracea was compared with a high-density monocrop, no differences were found in the ability of the female wasps to locate a host-infested plant, B. oleracea, infested with Plutella xylostella that was placed in the centre of the set-up. 4. The efficiency of the parasitoid to locate the host-infested plant was differentially affected by the species composition of the vegetation. Wasps entered the Sinapis-Brassica set-up faster, but took more time to find the host-infested plant than in the Hordeum-Brassica set-up. 5. The horizontal arrangement, i.e. by mixing S. alba or H. vulgare with, or placing them as rows between B. oleracea, did not affect host-finding efficiency. 6. Plant height did influence host finding. Wasps found the host-infested plants earlier in the set-up with short Sinapis plants compared with tall Sinapis plants. 7. Once the wasps had landed on the host-infested plant, the surrounding vegetation did not affect time needed to parasitize five consecutive hosts on the same infested plant, regardless of the composition or horizontal/vertical arrangement of the set-up. 8. Chemical and structural refuges in complex landscapes may play an important role in the persistence of this system through dampening oscillations of parasitoid and host populations
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