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.

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Early-season movement dynamics of phytophagous pest and natural enemies across a native vegetation-crop ecotone
Macfadyen, S. ; Hopkinson, J. ; Parry, H. ; Neave, M.J. ; Bianchi, F.J.J.A. ; Zalucki, M.P. ; Schellhorn, N.A. - \ 2015
Agriculture, Ecosystems and Environment 200 (2015). - ISSN 0167-8809 - p. 110 - 118.
managing ecosystem services - agricultural landscape - biological-control - spatial scales - dispersal - colonization - predators - ecology - parasitoids - suppression
There is limited understanding about how insect movement patterns are influenced by landscape features, and how landscapes can be managed to suppress pest phytophage populations in crops. Theory suggests that the relative timing of pest and natural enemy arrival in crops may influence pest suppression. However, there is a lack of data to substantiate this claim. We investigate the movement patterns of insects from native vegetation (NV) and discuss the implications of these patterns for pest control services. Using bi-directional interception traps we quantified the number of insects crossing an NV/crop ecotone relative to a control crop/crop interface in two agricultural regions early in the growing season. We used these data to infer patterns of movement and net flux. At the community-level, insect movement patterns were influenced by ecotone in two out of three years by region combinations. At the functional-group level, pests and parasitoids showed similar movement patterns from NV very soon after crop emergence. However, movement across the control interface increased towards the end of the early-season sampling period. Predators consistently moved more often from NV into crops than vice versa, even after crop emergence. Not all species showed a significant response to ecotone, however when a response was detected, these species showed similar patterns between the two regions. Our results highlight the importance of NV for the recruitment of natural enemies for early season crop immigration that may be potentially important for pest suppression. However, NV was also associated with crop immigration by some pest species. Hence, NV offers both opportunities and risks for pest management. The development of targeted NV management may reduce the risk of crop immigration by pests, but not of natural enemies.
Location and external characteristics of the Oecophylla smaragdina queen nest
Itterbeeck, J. Van; Sivongxay, N. ; Praxaysombath, B. ; Huis, A. van - \ 2015
Insectes Sociaux 62 (2015)3. - ISSN 0020-1812 - p. 351 - 356.
weaver ant oecophylla - hymenoptera-formicidae - biological-control - green ant - fabricius - colony - harvest - citrus
The Asian weaver ant Oecophylla smaragdina is of importance to Southeast Asian livelihoods as a source of human food and animal feed and as biological control agent in tree crops including mango and citrus. The introduction of weaver ants in plantations requires the inclusion of the reproductive queen. We report on locating the gravid queen in a mature O. smaragdina colony in Laos. The queen tree could be identified by considering tree height and number of nests in the tree: no tree was taller and housed more nests than the queen tree. The queen nest was a small nest, located near the tree top and near the trunk, and with more workers patrolling its exterior than at other small nests in the queen tree. The queen nest can be highly inconspicuous in dense tree crowns. Queen nest identification was ascertained by tapping and shaking nests, supporting branches, or entire trees, which elicits queen evacuation with retinue.
Legacy effects of anaerobic soil disinfestation on soil bacterial community composition and production of pathogen-suppressing volatiles
Os, G.J. van; Agtmaal, M. van; Hol, G. ; Hundscheid, M.P.J. ; Runia, W.T. ; Hordijk, C. ; Boer, W. de - \ 2015
Frontiers in Microbiology 6 (2015). - ISSN 1664-302X
pythium root-rot - soilborne plant-diseases - microbial-populations - organic amendments - biological-control - bulbous iris - fungistasis - growth - biocontrol - diversity
There is increasing evidence that microbial volatiles (VOCs) play an important role in natural suppression of soil-borne diseases, but little is known on the factors that influence production of suppressing VOCs. In the current study we examined whether a stress-induced change in soil microbial community composition would affect the production by soils of VOCs suppressing the plant-pathogenic oomycete Pythium. Using pyrosequencing of 16S ribosomal gene fragments we compared the composition of bacterial communities in sandy soils that had been exposed to anaerobic disinfestation (AD), a treatment used to kill harmful soil organisms, with the composition in untreated soils. Three months after the AD treatment had been finished, there was still a clear legacy effect of the former anaerobic stress on bacterial community composition with a strong increase in relative abundance of the phylum Bacteroidetes and a significant decrease of the phyla Acidobacteria, Planctomycetes, Nitrospirae, Chloroflexi, and Chlorobi. This change in bacterial community composition coincided with loss of production of Pythium suppressing soil volatiles (VOCs) and of suppression of Pythium impacts on Hyacinth root development. One year later, the composition of the bacterial community in the AD soils was reflecting that of the untreated soils. In addition, both production of Pythium-suppressing VOCs and suppression of Pythium in Hyacinth bioassays had returned to the levels of the untreated soil. GC/MS analysis identified several VOCs, among which compounds known to be antifungal, that were produced in the untreated soils but not in the AD soils. These compounds were again produced 15 months after the AD treatment. Our data indicate that soils exposed to a drastic stress can temporarily lose pathogen suppressive characteristics and that both loss and return of these suppressive characteristics and that both loss and return of these suppressive characteristics coincides with shifts in the soil bacterial community composition. Our data are supporting the suggested importance of microbial VOCs in the natural buffer of soils against diseases caused by soil-borne pathogens.
Enemies lost: parallel evolution in structural defense and tolerance to herbivory of invasive Jacobaea vulgaris
Lin, T. ; Doorduin, L. ; Temme, A. ; Pons, T.L. ; Lamers, G.E.M. ; Anten, N.P.R. ; Vrieling, K. - \ 2015
Biological Invasions 17 (2015)8. - ISSN 1387-3547 - p. 2339 - 2355.
nitrogen-use efficiency - increased competitive ability - leaf construction cost - pyrrolizidine alkaloids - senecio-jacobaea - united-states - generalist herbivores - biomass allocation - biological-control - sapium-sebiferum
According to the Shifting Defense Hypothesis, invasive plants should trade-off their costly quantitative defense to cheaper qualitative defense and growth due to the lack of natural specialist enemies and the presence of generalist enemies in the introduced areas. Several studies showed that plant genotypes from the invasive areas had a better qualitative defense than genotypes from the native area but only a few studies have focused on the quantitative defenses and tolerance ability. We compared structural defenses, tolerance and growth between invasive and native plant populations from different continents using the model plant Jacobaea vulgaris. We examined several microscopical structure traits, toughness, amount of cell wall proteins, growth and root-shoot ratio, which is a proxy for tolerance. The results show that invasive Jacobaea vulgaris have thinner leaves, lower leaf mass area, lower leaf cell wall protein contents and a lower root-shoot ratio than native genotypes. It indicates that invasive genotypes have poorer structural defense and tolerance to herbivory but potentially higher growth compared to native genotypes. These findings are in line with the Evolution of Increased Competitive Ability hypothesis and Shifting Defense Hypothesis. We also show that the invasiveness of this species in three geographically separated regions is consistently associated with the loss of parts of its quantitative defense and tolerance ability. The simultaneous change in quantitative defense and tolerance of the same magnitude and direction in the three nvasive regions can be explained by parallel evolution. We argue that such parallel evolution might be attributed to the absence of natural enemies rather than adaptation to local abiotic factors, since climate conditions among these three regions were different. Understanding such evolutionary changes helps to understand why plant species become invasive and might be important for biological control.
Early-season crop colonization by parasitoids is associated with native vegetation, but is spatially and temporally erratic
Bianchi, F.J.J.A. ; Walters, B.J. ; Hove, A.L.T. ; Cunningham, S.A. ; Werf, W. van der; Douma, J.C. ; Schellhorn, N.A. - \ 2015
Agriculture, Ecosystems and Environment 207 (2015). - ISSN 0167-8809 - p. 10 - 16.
terebrans hymenoptera-ichneumonidae - managing ecosystem services - biological-control - bemisia-tabaci - pest-control - agricultural landscapes - habitats - biodiversity - populations - arthropods
Semi-natural habitats in agricultural landscapes may support parasitoid populations that provide biocontrol services by suppressing populations of crop pests, but little is known about the spatial pattern and variability of these services at different levels of scale. Here we investigate the rarely studied phenomenon of early-season crop colonization by parasitoids and the relationship with the surrounding landscape. We assessed parasitism of whiteflies by placing whitefly infested cotton seedlings in remnant vegetation, arable land 25–125 m from remnant vegetation, and arable land further than 400 m from remnant vegetation. Twelve to twenty sentinel plants were exposed in a 25 × 25 m grid pattern in plots in each habitat. The experiment was conducted at 18 locations across two landscapes and repeated three times in a 2-week period in 2007 and 2008. Parasitism was observed during the first three days after the introduction of the whitefly infested seedlings and was in all cases caused by Encarsia spp. The mean number of parasitized whitefly per plant was 0.106 ± 0.025 and was highest on cotton plants placed in remnant vegetation, declining with increasing distance from remnant vegetation. A regression model with land use and meteorological variables received more statistical support from the data than models with only landscape and time period as factors. Parasitism levels were influenced by the proportion of remnant vegetation, grassland, as well as wind, temperature, dew point temperature and year. Early-season colonization of whitefly infested seedlings by parasitoids was erratic and characterized by large spatial (inter-plant and inter-plot) and temporal variation. Our study confirms that remnant vegetation function as reservoirs for parasitoids and that parasitoids can penetrate arable fields beyond 125 m within 3 days. However, variation in the occurrence of parasitism makes it difficult to predict parasitoid colonization at a specific place and time. Therefore, field-based scouting for pests and parasitoids is necessary, even in landscapes with a high biocontrol potential.
Analysis of microbial taxonomical groups present in maize stalks suppressive to colonization by toxigenic Fusarium spp.: A strategy for the identification of potential antagonists
Köhl, J. ; Lombaers-van der Plas, C.H. ; Moretti, A. ; Bandyopadhyay, R. ; Somma, S. ; Kastelein, P. - \ 2015
Biological Control 83 (2015). - ISSN 1049-9644 - p. 20 - 28.
biological-control - rhizosphere microbiome - quantitative detection - microdochium-bolleyi - acremonium-strictum - fungal antagonists - idriella-bolleyi - seed treatment - head blight - durum-wheat
Pink ear rot of maize caused by Fusarium verticillioides, Fusariumproliferatum and Fusariumgraminearumcan lead to severe yield losses and contamination of grain with a range of mycotoxins. Maize stalks colonized by Fusarium spp. are the main primary inoculum source for Fusarium incited epidemics in maize or other susceptible crops grown in rotation. The colonization of individual maize stalks originating from fields in The Netherlands, Italy and Nigeria byFusarium spp. was quantified using specific TaqMan-PCR assays. Highest values were found for F. graminearum and Fusariumavenaceum in Dutch samples, for F. graminearum and FUM producing species (F. verticillioides and F. proliferatum) in Italian samples and FUM producing Fusarium spp. in Nigerian samples. The increase in Fusarium spp. colonization under field conditions during a period of 3–6 months after harvest of the maize crops varied considerably between individual stalks. The fungal and bacterial diversity was analyzed for sub-sets of stalks with high versus low increase of Fusariumcolonization. Bacterial taxonomic groups such as Bacillus, Curtobacterium, Erwinia, Flavobacterium,Novosphingobium, Pantoea, Sphingomonas, Rahnella and Staphylococcus and fungal taxonomic groups such as Acremomium sp., Cryptococcus flavescens, Cryptococcus zeae, Leptosphaeria sp. andMicrodochium bolleyi were more abundant in the stalks with lower increase in pathogen colonization. Such fungal and bacterial groups associated with ‘suppressive stalks’ may be antagonistic to Fusarium spp. and a source of candidate strains for the selection of new biological control agents
Plant diversity and identity effects on predatory nematodes and their prey
Kostenko, O. ; Duyts, H. ; Grootemaat, S. ; Deyn, G.B. de; Bezemer, T.M. - \ 2015
Ecology and Evolution 5 (2015)4. - ISSN 2045-7758 - p. 836 - 847.
entomopathogenic nematodes - biological-control - biodiversity experiment - parasitic nematodes - food-web - soil - communities - grasslands - steinernema - populations
There is considerable evidence that both plant diversity and plant identity can influence the level of predation and predator abundance aboveground. However, how the level of predation in the soil and the abundance of predatory soil fauna are related to plant diversity and identity remains largely unknown. In a biodiversity field experiment, we examined the effects of plant diversity and identity on the infectivity of entomopathogenic nematodes (EPNs, Heterorhabditis and Steinernema spp.), which prey on soil arthropods, and abundance of carnivorous non-EPNs, which are predators of other nematode groups. To obtain a comprehensive view of the potential prey/food availability, we also quantified the abundance of soil insects and nonpredatory nematodes and the root biomass in the experimental plots. We used structural equation modeling (SEM) to investigate possible pathways by which plant diversity and identity may affect EPN infectivity and the abundance of carnivorous non-EPNs. Heterorhabditis spp. infectivity and the abundance of carnivorous non-EPNs were not directly related to plant diversity or the proportion of legumes, grasses and forbs in the plant community. However, Steinernema spp. infectivity was higher in monocultures of Festuca rubra and Trifolium pratense than in monocultures of the other six plant species. SEM revealed that legumes positively affected Steinernema infectivity, whereas plant diversity indirectly affected the infectivity of Heterorhabditis EPNs via effects on the abundance of soil insects. The abundance of prey (soil insects and root-feeding, bacterivorous, and fungivorous nematodes) increased with higher plant diversity. The abundance of prey nematodes was also positively affected by legumes. These plant community effects could not be explained by changes in root biomass. Our results show that plant diversity and identity effects on belowground biota (particularly soil nematode community) can differ between organisms that belong to the same feeding guild and that generalizations about plant diversity effects on soil organisms should be made with great caution.
Gac-mediated changes in pyrroloquinoline quinone biosynthesis enhance the antimicrobial activity of Pseudomonas fluorescens SBW25
Cheng, X. ; Voort, M. van der; Raaijmakers, J.M. - \ 2015
Environmental Microbiology Reports 7 (2015)1. - ISSN 1758-2229 - p. 139 - 147.
biological-control - systemic resistance - biocontrol bacteria - root-colonization - gluconic acid - brassicacearum - arabidopsis - derivatives - induction - pathogens
In Pseudomonas species, production of secondary metabolites and exoenzymes is regulated by the GacS/GacA two-component regulatory system. In P. fluorescens SBW25, mutations in the Gac-system cause major transcriptional changes and abolished production of the lipopeptide viscosin and of an exoprotease. In contrast to many other Pseudomonas species and strains, inactivation of the Gac-system in strain SBW25 significantly enhanced its antimicrobial activities against oomycete, fungal and bacterial pathogens. Here, random plasposon mutagenesis of the gacS mutant led to the identification of seven mutants with reduced or loss of antimicrobial activity. In four mutants, the plasposon insertion was located in genes of the pyrroloquinoline quinone (PQQ) biosynthesis pathway. Genetic complementation, ectopic expression, activity bioassays and RP-HPLC analyses revealed that a gacS mutation in SBW25 leads to enhanced expression of pqq genes, resulting in an increase in gluconic and 2-ketogluconic acid production, which in turn acidified the extracellular medium to levels that inhibit growth of other microorganisms. We also showed that PQQ-mediated acidification comes with a growth penalty for the gacS mutant in the stationary phase. In conclusion, PQQ-mediated acidification compensates for the loss of several antimicrobial traits in P. fluorescens SBW25 and may help gac mutants to withstand competitors.
The Freshwater Sponge Ephydatia fluviatilis Harbours Diverse Pseudomonas Species (Gammaproteobacteria, Pseudomonadales) with Broad-Spectrum Antimicrobial Activity
Keller-Costa, T. ; Jousset, A. ; Overbeek, L.S. van; Elsas, J.D. ; Costa, R. - \ 2014
PLoS ONE 9 (2014)2. - ISSN 1932-6203
fluorescent pseudomonads - secondary metabolites - phenotypic variation - bacterial symbiont - biological-control - biofilm formation - small rnas - sp nov. - rhizosphere - community
Bacteria are believed to play an important role in the fitness and biochemistry of sponges (Porifera). Pseudomonas species (Gammaproteobacteria, Pseudomonadales) are capable of colonizing a broad range of eukaryotic hosts, but knowledge of their diversity and function in freshwater invertebrates is rudimentary. We assessed the diversity, structure and antimicrobial activities of Pseudomonas spp. in the freshwater sponge Ephydatia fluviatilis. Polymerase Chain Reaction - Denaturing Gradient Gel Electrophoresis (PCR-DGGE) fingerprints of the global regulator gene gacA revealed distinct structures between sponge-associated and free-living Pseudomonas communities, unveiling previously unsuspected diversity of these assemblages in freshwater. Community structures varied across E. fluviatilis specimens, yet specific gacA phylotypes could be detected by PCR-DGGE in almost all sponge individuals sampled over two consecutive years. By means of whole-genome fingerprinting, 39 distinct genotypes were found within 90 fluorescent Pseudomonas isolates retrieved from E. fluviatilis. High frequency of in vitro antibacterial (49%), antiprotozoan (35%) and anti-oomycetal (32%) activities was found among these isolates, contrasting less-pronounced basidiomycetal (17%) and ascomycetal (8%) antagonism. Culture extracts of highly predation-resistant isolates rapidly caused complete immobility or lysis of cells of the protozoan Colpoda steinii. Isolates tentatively identified as P. jessenii, P. protegens and P. oryzihabitans showed conspicuous inhibitory traits and correspondence with dominant sponge-associated phylotypes registered by cultivation-independent analysis. Our findings suggest that E. fluviatilis hosts both transient and persistent Pseudomonas symbionts displaying antimicrobial activities of potential ecological and biotechnological value.
Species’ traits influence ground beetle responses to farm and landscape level agricultural intensification in Europe
Winqvist, C. ; Bengtsson, J. ; Öckinger, E. ; Aavik, T. ; Berendse, F. ; Clement, L.W. ; Geiger, F. - \ 2014
Journal of Insect Conservation 18 (2014)5. - ISSN 1366-638X - p. 837 - 846.
carabid beetle - habitat fragmentation - biological-control - intraguild predation - functional diversity - spatial scales - arable crops - context - biodiversity - land
Agricultural intensification may result in important shifts in insect community composition and function, but this remains poorly explored. Studying how groups of species with shared traits respond to local and landscape scale land-use management can reveal mechanisms behind such observed impacts. We tested if ground beetles (Coleoptera: Carabidae) divided into trait groups based on body sizes, wing morphologies and dietary preferences respond differently to farming practise (organic and conventional), farming intensity (measured as yield) and landscape complexity (measured as the proportion of arable land within a 1,000 m radius) across Europe. We used data from 143 farms in five regions in northern and central Europe. Organic farms did not differ in abundance or richness of any trait group compared to conventional farms. As farm scale intensity (yield) increased, overall abundance of beetles decreased, but abundances of small and medium sized beetles, as well as that of wingless beetles, were unaffected. Overall species richness was not affected by yield, whereas consideration of traits revealed that phytophagous and omnivorous beetles were less species rich on farms with high yields. Increasing the proportion of arable land in the landscape increased overall beetle abundance. This was driven by an increase in omnivorous beetles. The total species richness was not affected by an increase in the proportion arable land, although the richness of wingless beetles was found to increase. Potential effects on ecosystem functioning need to be taken into account when designing schemes to maintain agricultural biodiversity, because species with different ecological traits respond differently to local management and landscape changes.
Rearing of Microplitis mediator (Hymenoptera: Braconidae) and its host Mamestra brassicae (Lepidoptera: Noctuidae)
Belz, E. ; Géneau, C.E. ; Fürst, M. ; Balmer, O. ; Andermatt, P. ; Pfiffner, L. ; Westerd, L.E.C. ; Luka, H. - \ 2014
European Journal of Entomology 111 (2014)3. - ISSN 1210-5759 - p. 443 - 447.
olfactory attractiveness - biological-control - cabbage-looper - parasitoids - behavior - moth
Establishing continuous and reliable colonies of pest-parasitoid systems in the laboratory is an essential requirement for carrying out manipulative experiments on biological control. Here we describe in detail the rearing protocols that we optimized for the efficient rearing of the cabbage moth Mamestra brassicae and its key parasitoid Microplitis mediator.
Life-history analysis of Thaumastocoris peregrinus in a newly designed mass rearing strategy
Martínez, G. ; López, L. ; Cantero, G. ; González, A. ; Dicke, M. - \ 2014
Bulletin of Insectology 67 (2014)2. - ISSN 1721-8861 - p. 199 - 205.
noackae hymenoptera mymaridae - hemiptera thaumastocoridae - biological-control - invasive pest - 1st record - eucalyptus - heteroptera - brazil
The bronze bug, Thaumastocoris peregrinus Carpintero et Dellape (Heteroptera Thaumastocoridae), is one of the most important emerging pests of Eucalyptus LHeritier plantations worldwide. In the development of strategies to control this pest, establishing effective rearing protocols is fundamental to future research programs. We assessed life-history parameters of the bronze bug in a newly designed mass rearing strategy. Separated units were set up to contain different developmental stages. Egg production by females reared on commonly found Eucalyptus grandis Hill ex Maiden and Eucalyptus tereticornis Smith was evaluated in order to determine which plant species to use in rearing. Females laid more eggs on E. tereticornis than on E. grandis, so the former species was chosen for the rearing. A cohort of 207 eggs was followed in Petri dishes until the last individual died or reached the adult stage. We followed egg production by 15 adult couples from the original cohort. Preparation of 150-200 dishes with hatching eggs per week allows for an average production of 7,500 eggs per week. Under our rearing conditions, eggs started hatching on day six, and the first adults were obtained 23 days after oviposition. Almost half of the eggs did not hatch, and the highest nymphal mortality was recorded in the second instar, while the lowest mortality occurred in the last instar. We discuss the relevance of this mass rearing strategy, both within the context of basic behavioural studies of T. peregrinus, and as a tool for the mass rearing of the biological control agent, Cleruchoides noackae Lin et Huber.
Response of the zoophytophagous predators Macrolophus pygmaeus and Nesidiocoris tenuis to volatiles of uninfested plants and to plants infested by prey or conspecifics
Lins, J.C. ; Loon, J.J.A. van; Bueno, V.H.P. ; Lucas-Barbosa, D. ; Dicke, M. ; Lenteren, J.C. van - \ 2014
BioControl 59 (2014)6. - ISSN 1386-6141 - p. 707 - 718.
borer tuta-absoluta - carnivorous arthropods - heteroptera miridae - biological-control - infochemical use - spider-mites - tomato - herbivores - bug - caliginosus
Knowledge about the orientation mechanisms used by two important predaceous mirids (Macrolophus pygmaeus Rambour and Nesidiocoris tenuis (Reuter)) in finding their prey (whitefly Bemisia tabaci (Gennadius) and the tomato borer Tuta absoluta (Meyrick)) is limited. In a Y-tube olfactometer, we tested the behavioral responses of naïve and experienced predators to uninfested plants, herbivore-induced plant volatiles (HIPVs) from plants infested with T. absoluta and/or B. tabaci, the sex pheromone of T. absoluta, and volatiles produced by plants injured by the predators. Nesidiocoris tenuis responds to volatiles produced by uninfested plants only after experience with the plant, whereas naïve and experienced M. pygmaeus show positive chemotaxis. Both predators are attracted to volatiles from prey-infested plants, and we provide the first evidence that experience affects this response in M. pygmaeus. Infestation of the same plant by both prey species elicited similar responses by the two predators as plants infested by either herbivore singly. Neither predator responded to sex pheromones of T. absoluta. Macrolophus pygmaeus avoided plants injured by conspecifics, while N. tenuis females were attracted by such plants. The implications of these results for augmentative biological control are discussed.
Feeding preferences of the aphidophagous hoverfly Sphaerophoria rueppellii affect the performance of its offspring
Amorós-Jiménez, R. ; Pineda Gomez, A.M. ; Fereres, A. ; Marcos-García, M.A. - \ 2014
BioControl 59 (2014)4. - ISSN 1386-6141 - p. 427 - 435.
episyrphus-balteatus diptera - sweet-pepper greenhouses - biological-control - hymenopteran parasitoids - floral resources - insectary plants - natural enemies - cereal aphids - host-plant - body-size
Provision of additional floral resources in the crop is a successful strategy of conservation biological control for attracting several natural enemies including predatory syrphids. However, the selection of flower species is mainly based on visiting preferences, paying little attention to the link between preference and performance. In this study, we assess the influence of feeding on flowers of two insectary plants (sweet alyssum and coriander) and flowers of a crop species (sweet pepper) on performance of the parental and first generation of the syrphid Sphaerophoria rueppellii (Wiedemann) (Diptera: Syrphidae). We found that floral preference of the adults was linked to developmental performance of their offspring. Sweet alyssum was the flower most frequently visited by syrphid adults, enhancing adult body size and egg-to adult survival of the F1 generation.
Coupled human and natural system dynamics as key to the sustainability of Lake Victoria’s ecosystem services
Downing, A.S. ; Nes, E.H. van; Balirwa, J.S. ; Beuving, J. ; Bwathondi, P.O.J. ; Chapman, L.J. ; Cornelissen, I.J.M. ; Cowx, I.G. ; Goudswaard, P.C. ; Hecky, R.E. ; Janse, J.H. ; Janssen, A.B.G. ; Kaufman, L. ; Kishe-Machumu, M.A. ; Kolding, J. ; Ligtvoet, W. ; Mbabazi, D. ; Medard, M. ; Mkumbo, O.C. ; Mlaponi, E. ; Munyaho, A.T. ; Nagelkerke, L.A.J. ; Ogutu-Ohwayo, R. ; Ojwang, W.O. ; Peter, H.K. ; Schindler, D.E. ; Seehausen, O. ; Sharpe, D. ; Silsbe, G.M. ; Sitoki, L. ; Tumwebaze, R. ; Tweddle, D. ; Wolfshaar, K.E. van de; Dijk, J.W.M. van; Donk, E. van; Rijssel, J.C. van; Zwieten, P.A.M. van; Wanink, J. ; Witte, F. ; Mooij, W.M. - \ 2014
Ecology and Society 19 (2014)4. - ISSN 1708-3087
cyprinid rastrineobola-argentea - perch lates-niloticus - nile perch - east-africa - water hyacinth - mwanza gulf - oreochromis-niloticus - morphological-changes - introduced predator - biological-control
East Africa’s Lake Victoria provides resources and services to millions of people on the lake’s shores and abroad. In particular, the lake’s fisheries are an important source of protein, employment, and international economic connections for the whole region. Nonetheless, stock dynamics are poorly understood and currently unpredictable. Furthermore, fishery dynamics are intricately connected to other supporting services of the lake as well as to lakeshore societies and economies. Much research has been carried out piecemeal on different aspects of Lake Victoria’s system; e.g., societies, biodiversity, fisheries, and eutrophication. However, to disentangle drivers and dynamics of change in this complex system, we need to put these pieces together and analyze the system as a whole. We did so by first building a qualitative model of the lake’s social-ecological system. We then investigated the model system through a qualitative loop analysis, and finally examined effects of changes on the system state and structure. The model and its contextual analysis allowed us to investigate system-wide chain reactions resulting from disturbances. Importantly, we built a tool that can be used to analyze the cascading effects of management options and establish the requirements for their success. We found that high connectedness of the system at the exploitation level, through fisheries having multiple target stocks, can increase the stocks’ vulnerability to exploitation but reduce society’s vulnerability to variability in individual stocks. We describe how there are multiple pathways to any change in the system, which makes it difficult to identify the root cause of changes but also broadens the management toolkit. Also, we illustrate how nutrient enrichment is not a self-regulating process, and that explicit management is necessary to halt or reverse eutrophication. This model is simple and usable to assess system-wide effects of management policies, and can serve as a paving stone for future quantitative analyses of system dynamics at local scales.
Reciprocal interactions between native and introduced populations of common milkweed, Asclepias syriaca, and the specialist aphid, Aphis nerii
Bukovinszky, T. ; Gols, R. ; Agrawal, A.A. ; Roge, C. ; Bezemer, T.M. ; Biere, A. ; Harvey, J.A. - \ 2014
Basic and Applied Ecology 15 (2014)5. - ISSN 1439-1791 - p. 444 - 452.
oleander aphid - biological-control - density-dependence - genetic-variation - local adaptation - natural enemies - invasive plants - host plants - herbivores - evolution
Following its introduction into Europe (EU), the common milkweed (Asclepias syriaca) has been free of most specialist herbivores that are present in its native North American (NA) range, except for the oleander aphid Aphis nerii. We compared EU and NA populations of A. nerii on EU and NA milkweed populations to test the hypothesis that plant–insect interactions differ on the two continents. First, we tested if herbivore performance is higher on EU plants than on NA plants, because the former have escaped most of their herbivores and have perhaps been selected for lower defence levels following introduction. Second, we compared two A. nerii lines (one from each continent) to test whether genotypic differences in the herbivore may influence species interactions in plant–herbivore communities in the context of species introductions. The NA population of A. nerii developed faster, had higher fecundity and attained higher population growth rates than the EU population. There was no overall significant continental difference in aphid resistance between the plants. However, milkweed plants from EU supported higher population growth rates and faster development of the NA line of A. nerii than plants from NA. In contrast, EU aphids showed similar (low) performance across plant populations from both continents. In a second experiment, we examined how chewing herbivores indirectly mediate interactions between milkweeds and aphids, and induced A. syriaca plants from each continent by monarch caterpillars (Danaus plexippus) to compare the resulting changes in plant quality on EU aphid performance. As specialist chewing herbivores of A. syriaca are only present in NA, we expected that plants from the two continents may affect aphid growth in different ways when they are challenged by a specialist chewing herbivore. Caterpillar induction decreased aphid developmental times on NA plants, but not on EU plants, whereas fecundity and population growth rates were unaffected by induction on both plant populations. The results show that genetic variation in the plants as well as in the herbivores can determine the outcome of plant–herbivore interactions.
Unravelling the microbiome of eggs of the endangered sea turtle Eretmochelys imbricata identifies bacteria with activity against the emerging pathogen Fusarium falciforme
Sarmiento-Ramírez, J.M. ; Voort, M. van der; Raaijmakers, J.M. ; Diéguez-Uribeondo, J. - \ 2014
PLoS ONE 9 (2014)4. - ISSN 1932-6203 - 8 p.
caretta-caretta - biological-control - gut microbiota - dna-sequences - costa-rica - streptomyces - diseases - community - fungal - health
Habitat bioaugmentation and introduction of protective microbiota have been proposed as potential conservation strategies to rescue endangered mammals and amphibians from emerging diseases. For both strategies, insight into the microbiomes of the endangered species and their habitats is essential. Here, we sampled nests of the endangered sea turtle species Eretmochelys imbricata that were infected with the fungal pathogen Fusarium falciforme. Metagenomic analysis of the bacterial communities associated with the shells of the sea turtle eggs revealed approximately 16,664 operational taxonomic units, with Proteobacteria, Actinobacteria, Firmicutes and Bacteroidetes as the most dominant phyla. Subsequent isolation of Actinobacteria from the eggshells led to the identification of several genera (Streptomyces, Amycolaptosis, Micromomospora Plantactinospora and Solwaraspora) that inhibit hyphal growth of the pathogen F. falciforme. These bacterial genera constitute a first set of microbial indicators to evaluate the potential role of microbiota in conservation of endangered sea turtle species.
Increased control of thrips and aphids in greenhouses with two species of generalist predatory bugs involved in intraguild predation
Messelink, G.J. ; Janssen, A. - \ 2014
Biological Control 79 (2014). - ISSN 1049-9644 - p. 1 - 7.
macrolophus-pygmaeus hemiptera - biological-control - myzus-persicae - nesidiocoris-tenuis - tuta-absoluta - pepper plants - prey - heteroptera - miridae - communities
The combined release of species of generalist predators can enhance multiple pest control when the predators feed on different prey, but, in theory, predators may be excluded through predation on each other. This study evaluated the co-occurrence of the generalist predators Macrolophus pygmaeus Rambur and Orius laevigatus (Fieber) and their control of two pests in a sweet pepper crop. Both predators consume pollen and nectar in sweet pepper flowers, prey on thrips and aphids, and O. laevigatus is an intraguild predator of M. pygmaeus. Observations in a commercial sweet pepper crop in a greenhouse with low densities of pests showed that the two predator species coexisted for 8 months. Moreover, their distributions in flowers suggested that they were neither attracted to each other, nor avoided or excluded each other. A greenhouse experiment showed that the predators together clearly controlled thrips and aphids better than each of them separately. Thrips control was significantly better in the presence of O. laevigatus and aphid control was significantly better in the presence of M. pygmaeus. Hence, combined inoculative releases of M. pygmaeus and O. laevigatus seem to be a good solution for controlling both thrips and aphids in greenhouse-grown sweet pepper. The predators are able to persist in one crop for a sufficiently long period and they complement each other in the control of both pests. This study also provides further evidence that intraguild predation does not necessarily have negative effects on biological control.
Long-term effects of eight soil health treatments to control plant-parasitic nematodes and Verticillium dahliae in agro-ecosystems
Korthals, G.W. ; Thoden, T.C. ; Berg, W. van den; Visser, J.H.M. - \ 2014
Applied Soil Ecology 76 (2014). - ISSN 0929-1393 - p. 112 - 123.
root-knot nematode - pratylenchus-penetrans - meloidogyne-hapla - tagetes-patula - nitrogen mineralization - biological-control - damping-off - cover crops - pyrrolizidine alkaloids - glucosinolate-profiles
There is an urgent need to test and develop sustainable methods for management of soil pathogens, such as the root-lesion nematode Pratylenchus penetrans and the soil fungus Verticillium dahliae. Ultimately this should be investigated with a multidisciplinary approach, with long-term measurements of biological and chemical parameters and their final impact on crop yield under field conditions. The present study focusses on eight soil health treatments (compost, chitin, marigold, grass–clover, biofumigation, anearobic soil disinfestation, a physical control method and a combination of marigold, compost and chitin) and two control treatments (a chemical control with 300 L/ha Metam sodium and un untreated control). These 10 treatments were studied for their effects on soil chemical quality, soil pathogens and their impact on the yield of potato, lily and carrots during 6 years. The present study did demonstrate that in comparison to chemical control, additions of chitin, anaerobic soil disinfestation and marigold are already excellent alternatives for the control of plant-parasitic nematodes and V. dahliae. We also demonstrated that grass–clover, biofumigation, Cultivit and compost are not effective alternatives for chemical control yet and further development is needed. All treatments caused a yield increase in comparison with the control. The biggest increases of more than 60% were found for the treatments with chitin. Furthermore it was demonstrated that these yield increases were probably less influenced by changes in chemical soil properties, but the consequence of changes in the soil biota, in this case especially the effective control of P. penetrans and V. dahliae. Furthermore it has been demonstrated that most of these soil health treatments could already be implemented in an arable crop rotation and probably adapted for many areas of the world where other alternatives, such as solarisation or soil flooding, are not feasible or too risky.
Infectious disease agents mediate interaction in food webs and ecosystems
Selakovic, S. ; Ruiter, P.C. de; Heesterbeek, J.A.P. - \ 2014
Proceedings of the Royal Society. B: Biological Sciences 281 (2014)1777. - ISSN 0962-8452 - 11 p.
biological-control - population-dynamics - species-diversity - mustela-nigripes - canine-distemper - african lions - host behavior - coral-reef - parasites - communities
Infectious agents are part of food webs and ecosystems via the relationship with their host species that, in turn, interact with both hosts and non-hosts. Through these interactions, infectious agents influence food webs in terms of structure, functioning and stability. The present literature shows a broad range of impacts of infectious agents on food webs, and by cataloguing that range, we worked towards defining the various mechanisms and their specific effects. To explore the impact, a direct approach is to study changes in food-web properties with infectious agents as separate species in the web, acting as additional nodes, with links to their host species. An indirect approach concentrates not on adding new nodes and links, but on the ways that infectious agents affect the existing links across host and non-host nodes, by influencing the 'quality' of consumer-resource interaction as it depends on the epidemiological state host involved. Both approaches are natural from an ecological point of view, but the indirect approach may connect more straightforwardly to commonly used tools in infectious disease dynamics.
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