Jetske de Boer

Dr. ir. Jetske de Boer PhD

Lecturer | Researcher
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Visiting Address

Droevendaalsesteeg 10
6708 PB Wageningen

+31 (0) 317 47 34 00

The Netherlands



Many insect species are declining globally, while some species cause problems as crop pests or for public health. This apparent insect-dilemma and its ecological solutions form the core of my research. I also use it as a tool in ecology education.


Insects play vital roles in all of our ecosystems. They are crucial in nature and agriculture by pollinating plants and as natural enemies of pest insects amongst their many other functions. I am particularly fascinated by the intriguing behaviours of insects and their intricate relationships with other organisms.

I did my PhD at Wageningen University on prey search behaviour of predatory mites (2004). The following years I studied genetics and behaviour of Cotesia parasitoids in relation to their sex determination mechanism (at the University of Minnesota and then at Groningen University ). In 2012, I returned to Wageningen to work on the interactions between malaria parasites, humans and mosquitoes. Together with two PhD students, we found that body odours of malaria-infected humans change in such a way that more mosquitoes are attracted.

In 2017, I joined the NIOO-KNAW. I first worked with Louise Vet on chemical ecology and behaviour of hyperparasitoids. These small insects are in the fourth trophic level and can disrupt biological control of aphids in sweet pepper greenhouses by killing the natural enemies that growers release (aphid parasitoids). Since 2020, I have a joint position as researcher at the NIOO and lector (professor of applied sciences) at the Aeres University of Applied Sciences, situated next to NIOO (…). My research focuses on ecological solutions for pest insect control (see project Smart parasitoids) and restoration of insect populations in various landscapes (in cities as well as in agriculture).

Research groups


Editorial board memberships

  • 2019–Present
    Entomologia Experimentalis et Applicata
  • 2012–Present
    Entomologische Berichten

Ancillary activities

  • Lector

    - current
    Lector at Aeres University of Applied Sciences


Peer-reviewed publications

  • Ecological Monographs

    Scientists' warning on climate change and insects

    Jeff A. Harvey, Kévin Tougeron, Rieta Gols, Robin Heinen, Mariana Abarca, Paul K. Abram, Yves Basset, Matty P. Berg, Carol Boggs, Jacques Brodeur, Pedro Cardoso, Jetske G. de Boer, Geert de Snoo, Charl Deacon, Jane E. Dell, Nicolas Desneux, Michael E. Dillon, Grant A. Duffy, Lee A. Dyer, Jacintha Ellers, Anahí Espíndola, James Fordyce, Matthew L. Forister, Caroline Fukushima, Matthew J. G. Gage, Carlos García‐Robledo, Claire Gely, Mauro Gobbi, Caspar A Hallmann, Thierry Hance, John Harte, Axel Hochkirch, Christian Hof, Ary A. Hoffmann, Joel G. Kingsolver, Greg P. A. Lamarre, William F Laurance, Blas Lavandero, Simon R Leather, Philipp Lehmann, Cécile Le Lann, Margarita M. López‐Uribe, Chun‐Sen Ma, Gang Ma, Joffrey Moiroux, Lucie Monticelli, Chris Nice, Paul J. Ode, Sylvain Pincebourde, William J. Ripple, Melissah Rowe, Michael J Samways, Arnaud Sentis, Alisha A. Shah, Nigel Stork, John S. Terblanche, Maddy Thakur, Matthew B. Thomas, Jason M. Tylianakis, Joan Van Baaren, Martijn van de Pol, Wim H. van der Putten, Hans Van Dyck, Wilco C. E. P. Verberk, David L Wagner, Wolfgang W. Weisser, William C. Wetzel, H. Arthur Woods, Kris A G Wyckhuys, Steven L Chown
    Climate warming is considered to be among the most serious of anthropogenicstresses to the environment, because it not only has direct effects on biodiver-sity, but it also exacerbates the harmful effects of other human-mediated threats. The associated consequences are potentially severe, particularly interms of threats to species preservation, as well as in the preservation of anarray of ecosystem services provided by biodiversity. Among the most affectedgroups of animals are insects—central components of many ecosystems—forwhich climate change has pervasive effects from individuals to communities.In this contribution to the scientists’warning series, we summarize the effectof the gradual global surface temperature increase on insects, in terms ofphysiology, behavior, phenology, distribution, and species interactions, as wellas the effect of increased frequency and duration of extreme events such as hotand cold spells, fires, droughts, and floods on these parameters. We warn that,if no action is taken to better understand and reduce the action of climatechange on insects, we will drastically reduce our ability to build a sustainablefuture based on healthy, functional ecosystems. We discuss perspectives onrelevant ways to conserve insects in the face of climate change, and we offerseveral key recommendations on management approaches that can beadopted, on policies that should be pursued, and on the involvement of thegeneral public in the protection effort.
  • Annual Review of Entomology

    The Ecology of Hyperparasitoids

    Erik H. Poelman, Antonino Cusumano, Jetske G. de Boer

    Hyperparasitoids are some of the most diverse members of insect food webs. True hyperparasitoids parasitize the larvae of other parasitoids, reaching these larvae with their ovipositor through the herbivore that hosts the parasitoid larva. During pupation, primary parasitoids also may be attacked by pseudohyperparasitoids that lay their eggs on the parasitoid (pre)pupae. By attacking primary parasitoids, hyperparasitoids may affect herbivore population dynamics, and they have been identified as a major challenge in biological control. Over the past decades, research, especially on aphid- and caterpillar-associated hyperparasitoids, has revealed that hyperparasitoids challenge rules on nutrient use efficiency in trophic chains, account for herbivore outbreaks, or stabilize competitive interactions in lower trophic levels, and they may use cues derived from complex interaction networks to locate their hosts. This review focuses on the fascinating ecology of hyperparasitoids related to how they exploit and locate their often inconspicuous hosts and the insect community processes in which hyperparasitoids are prominent players.
  • Ecological Entomology

    Effects of oviposition in a non-host species on foraging behaviour of the parasitoid Cotesia glomerata

    Jessica de Bruijn, Louise E.M. Vet, Hans M. Smid, Jetske G. de Boer

    Parasitoids lay their eggs in or on a host, usually another insect. During foraging, parasitoids can encounter insects that differ in terms of host suitability and quality. At one extreme end of this spectrum are non-hosts that are unsuitable for offspring development. Non-hosts are generally ignored but parasitization does occur and occasionally also results in egg deposition. Here, the authors investigate how oviposition in a non-host influences subsequent foraging behaviour of a parasitoid and whether this is mediated by learning. The study system consists of the endoparasitoid Cotesia glomerata and the presumed non-host caterpillar Mamestra brassicae. In the presence of Pieris brassicae hosts and/or their traces (frass), C. glomerata inserted its ovipositor into M. brassicae caterpillars. Eggs were deposited, but all eggs disappeared within 96 h, confirming the non-host status of M. brassicae. In contrast to the expectation, there was no memory retention after oviposition in a non-host and parasitoids did not alter their behaviour with respect to non-host contacts and ovipositions. Instead, C. glomerata became more motivated to forage on a non-host infested leaf. The authors propose that egg deposition in non-hosts by C. glomerata might be due to their high egg load, which is thought to make parasitoids less selective on host quality, especially when they have few reproductive opportunities. In such cases, fitness costs to individual females are low. Egg deposition in non-hosts might ultimately lead to host range expansion if parasitoids overcome the defence response of non-hosts over evolutionary time.
  • Journal of Chemical Ecology

    Avoidance of the Plant Hormone Cis-Jasmone by Aedes aegypti Depends On Mosquito Age in Both Plant and Human Odor Backgrounds

    Jetske G. de Boer, Aron P.S. Kuiper, Joeri Groot, Joop J.A. van Loon

    Adults of many mosquito species feed on plants to obtain metabolic energy and to enhance reproduction. Mosquitoes primarily rely on olfaction to locate plants and are known to respond to a range of plant volatiles. We studied the olfactory response of the yellow fever mosquito Aedes aegypti to methyl jasmonate (MeJA) and cis-jasmone (CiJA), volatile compounds originating from the octadecanoid signaling pathway that plays a key role in plant defense against herbivores. Specifically, we investigated how Ae. aegypti of different ages responded to elevated levels of CiJA in two attractive odor contexts, either derived from Lima bean plants or human skin. Aedes aegypti females landed significantly less often on a surface with CiJA and MeJA compared to the solvent control, CiJA exerting a stronger reduction in landing than MeJA. Odor context (plant or human) had no significant main effect on the olfactory responses of Ae. aegypti females to CiJA. Mosquito age significantly affected the olfactory response, older females (7–9 d) responding more strongly to elevated levels of CiJA than young females (1–3 d) in either odor context. Our results show that avoidance of CiJA by Ae. aegypti is independent of odor background, suggesting that jasmonates are inherently aversive cues to these mosquitoes. We propose that avoidance of plants with elevated levels of jasmonates is adaptive to mosquitoes to reduce the risk of encountering predators that is higher on these plants, i.e. by avoiding ‘enemy-dense-space’.
  • Communications Biology

    Chromosomal scale assembly of parasitic wasp genome reveals symbiotic virus colonization

    Jérémy Gauthier, Hélène Boulain, Joke Van Vugt, Lyam Baudry, Emma Persyn, Jean-Marc Aury, Benjamin Noel, Anthony Bretaudeau, Fabrice Legeai, Sven Warris, Mohamed A Chebbi, Géraldine Dubreuil, Bernard Duvic, Natacha Kremer, Philippe Gayral, Karine Musset, Thibaut Josse, Diane Bigot, Christophe Bressac, Sébastien Moreau, Georges Periquet, Myriam Harry, Nicolas Montagné, Isabelle Boulogne, Mahnaz Sabeti-Azad, Martine Maïbèche, Thomas Chertemps, Frédérique Hilliou, David Siaussat, Joëlle Amselem, Isabelle Luyten, Claire Capdevielle-Dulac, Karine Labadie, Bruna Laís Merlin, Valérie Barbe, Jetske G. de Boer, Martial Marbouty, Fernando Luis Cônsoli, Stéphane Dupas, Aurélie Hua-Van, Gaelle Le Goff, Annie Bézier, Emmanuelle Jacquin-Joly, James B Whitfield, Louise E.M. Vet, Hans M. Smid, Laure Kaiser, Romain Koszul, Elisabeth Huguet, Elisabeth A Herniou, Jean-Michel Drezen

    Endogenous viruses form an important proportion of eukaryote genomes and a source of novel functions. How large DNA viruses integrated into a genome evolve when they confer a benefit to their host, however, remains unknown. Bracoviruses are essential for the parasitism success of parasitoid wasps, into whose genomes they integrated ~103 million years ago. Here we show, from the assembly of a parasitoid wasp genome at a chromosomal scale, that bracovirus genes colonized all ten chromosomes of Cotesia congregata. Most form clusters of genes involved in particle production or parasitism success. Genomic comparison with another wasp, Microplitis demolitor, revealed that these clusters were already established ~53 mya and thus belong to remarkably stable genomic structures, the architectures of which are evolutionary constrained. Transcriptomic analyses highlight temporal synchronization of viral gene expression without resulting in immune gene induction, suggesting that no conflicts remain between ancient symbiotic partners when benefits to them converge.
  • Behavioral Ecology

    Memory extinction and spontaneous recovery shaping parasitoid foraging behavior

    Jessica de Bruijn, Louise E.M. Vet, Hans M. Smid, Jetske G. de Boer

    Animals can alter their foraging behavior through associative learning, where an encounter with an essential resource (e.g., food or a reproductive opportunity) is associated with nearby environmental cues (e.g., volatiles). This can subsequently improve the animal's foraging efficiency. However, when these associated cues are encountered again, the anticipated resource is not always present. Such an unrewarding experience, also called a memory-extinction experience, can change an animal's response to the associated cues. Although some studies are available on the mechanisms of this process, they rarely focus on cues and rewards that are relevant in an animal's natural habitat. In this study, we tested the effect of different types of ecologically relevant memory-extinction experiences on the conditioned plant volatile preferences of the parasitic wasp Cotesia glomerata that uses these cues to locate its caterpillar hosts. These extinction experiences consisted of contact with only host traces (frass and silk), contact with nonhost traces, or oviposition in a nonhost near host traces, on the conditioned plant species. Our results show that the lack of oviposition, after contacting host traces, led to the temporary alteration of the conditioned plant volatile preference in C. glomerata, but this effect was plant species-specific. These results provide novel insights into how ecologically relevant memory-extinction experiences can fine-tune an animal's foraging behavior. This fine-tuning of learned behavior can be beneficial when the lack of finding a resource accurately predicts current, but not future foraging opportunities. Such continuous reevaluation of obtained information helps animals to prevent maladaptive foraging behavior.
  • Journal of Animal Ecology

    Multi‐camera field monitoring reveals costs of learning for parasitoid foraging behaviour

    Jessica de Bruijn, Ilka Vosteen, Louise E.M. Vet, Hans M. Smid, Jetske G. de Boer
    1. Dynamic conditions in nature have led to the evolution of behavioural traits that allow animals to use information on local circumstances and adjust their behaviour accordingly, for example through learning. Although learning can improve foraging efficiency, the learned information can become unreliable as the environment continues to change. This could lead to potential fitness costs when memories holding such unreliable information persist. Indeed, persistent unreliable memory was found to reduce the foraging efficiency of the parasitoid Cotesia glomerata under laboratory conditions.

    2. Here, we evaluated the effect of such persistent unreliable memory on the foraging behaviour of C. glomerata in the field. This is a critical step in studies of foraging theory, since animal behaviour evolved under the complex conditions present in nature.

    3. Existing methods provide little detail on how parasitoids interact with their environment in the field, therefore we developed a novel multi‐camera system that allowed us to trace parasitoid foraging behaviour in detail. With this multi‐camera system, we studied how persistent unreliable memory affected the foraging behaviour of C. glomerata when these memories led parasitoids to plants infested with non‐host caterpillars in a semi‐field set‐up.

    4. Our results demonstrate that persistent unreliable memory can lead to maladaptive foraging behaviour in C. glomerata under field conditions and increased the likelihood of oviposition in the non‐host caterpillar Mamestra brassica. Furthermore, these time‐ and egg‐related costs can be context‐dependent, since they rely on the plant species used.

    5. These results provide us with new insight on how animals use previously obtained information in naturally complex and dynamic foraging situations and confirm that costs and benefits of learning depend on the environment animals forage in. Although behavioural studies of small animals in natural habitats remain challenging, novel methods such as our multi‐camera system contribute to understanding the nuances of animal foraging behaviour.
  • Pest Management Science

    Exploiting chemical ecology to manage hyperparasitoids in biological control of arthropod pests

    Antonino Cusumano, Jeff A. Harvey, Mitchel E. Bourne, Erik H. Poelman, Jetske G. de Boer
    Insect hyperparasitoids are fourth trophic level organisms that commonly occur in terrestrial food webs, yet they are relatively understudied. These top‐carnivores can disrupt biological pest control by suppressing the populations of their parasitoid hosts, leading to pest outbreaks, especially in confined environments such as greenhouses where augmentative biological control is used. There is no effective eco‐friendly strategy that can be used to control hyperparasitoids. Recent advances in the chemical ecology of hyperparasitoid foraging behavior have opened opportunities for manipulating these top‐carnivores in such a way that biological pest control becomes more efficient. We propose various infochemical‐based strategies to manage hyperparasitoids. We suggest that a push‐pull strategy could be a promising approach to ‘push’ hyperparasitoids away from their parasitoid hosts and ‘pull’ them into traps. Additionally, we discuss how infochemicals can be used to develop innovative tools improving biological pest control (i) to restrict accessibility of resources (e.g. sugars and alternative hosts) to primary parasitoid only or (ii) to monitor hyperparasitoid presence in the crop for early detection. We also identify important missing information in order to control hyperparasitoids and outline what research is needed to reach this goal. Testing the efficacy of synthetic infochemicals in confined environments is a crucial step towards the implementation of chemical ecology‐based approaches targeting hyperparasitoids. © 2019 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.
  • Ecological Entomology

    Honeydew composition and its effect on life-history parameters of hyperparasitoids

    Frank A,C. van Neerbos, Jetske G. de Boer, Lucia Salis, W. Tollenaar, Martine Kos, Louise E.M. Vet, Jeff A. Harvey
    1. Diets that maximise life span often differ from diets that maximise reproduction. Animals have therefore evolved advanced foraging strategies to acquire optimal nutrition and maximise their fitness. The free-living adult females of parasitoid wasps (Hymenoptera) need to balance their search for hosts to reproduce and for carbohydrate resources to feed. 2. Honeydew, excreted by phloem-feeding insects, presents a widely available carbohydrate source in nature that can benefit natural enemies of honeydew-producing insects. However, the effects of variation in honeydew on organisms in the fourth trophic level, such as hyperparasitoids, are not yet understood. 3. This study examined how five different honeydew types influence longevity and fecundity of four hyperparasitoid taxa. Asaphes spp. (Pteromalidae) and Dendrocerus spp. (Megaspilidae) are secondary parasitoids of aphid parasitoids and are thus associated with honeydew-producing insects. Gelis agilis and Acrolyta nens (both Ichneumonidae) are secondary parasitoids of species that do not use honeydew-producing hosts. 4. Most honeydew types had a positive or neutral effect on life span and fecundity of hyperparasitoids compared with controls without honeydew, although negative effects were also found for both aphid hyperparasitoids. Honeydew produced by aphids feeding on sweet pepper plants was most beneficial for all hyperparasitoid taxa, which can partially be explained by the high amount of honeydew, but also by the composition of dietary sugars in these honeydew types. 5. The findings of this study underline the value of aphid honeydew as a carbohydrate resource for fourth-trophic-level organisms, not only those associated with honeydew-producing insects but also ?interlopers? without such a natural association.
  • Insects

    Range-expansion in processionary moths and biological control

    Global climate change is resulting in a wide range of biotic responses, including changes in diel activity and seasonal phenology patterns, range shifts polewards in each hemisphere and/or to higher elevations, and altered intensity and frequency of interactions between species in ecosystems. Oak (Thaumetopoea processionea) and pine (T. pityocampa) processionary moths (hereafter OPM and PPM, respectively) are thermophilic species that are native to central and southern Europe. The larvae of both species are gregarious and produce large silken ‘nests’ that they use to congregate when not feeding. During outbreaks, processionary caterpillars are capable of stripping foliage from their food plants (oak and pine trees), generating considerable economic damage. Moreover, the third to last instar caterpillars of both species produce copious hairs as a means of defence against natural enemies, including both vertebrate and invertebrate predators, and parasitoids. These hairs contain the toxin thaumetopoein that causes strong allergic reactions when it comes into contact with human skin or other membranes. In response to a warming climate, PPM is expanding its range northwards, while OPM outbreaks are increasing in frequency and intensity, particularly in northern Germany, the Netherlands, and southern U.K., where it was either absent or rare previously. Here, we discuss how warming and escape from co-evolved natural enemies has benefitted both species, and suggest possible strategies for biological control. View Full-Text. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
  • Functional Ecology

    Volatiles of bacteria associated with parasitoid habitats elicit distinct olfactory responses in an aphid parasitoid and its hyperparasitoid

    Tim Goelen, Islam S. Sobhy, Christophe Vanderaa, Jetske G. de Boer, Frank Delvigne, Frédéric Francis, Felix Wäckers, Hans Rediers, Kevin J. Verstrepen, Tom Wenseleers, Hans Jacquemyn, Bart Lievens
    Abstract To locate mating partners and essential resources such as food, oviposition sites and shelter, insects rely to a large extent on chemical cues. While most research has focused on cues derived from plants and insects, there is mounting evidence that indicates that micro-organisms emit volatile compounds that may play an important role in insect behaviour. In this study, we assessed how volatile compounds emitted by phylogenetically diverse bacteria affected the olfactory response of the primary parasitoid Aphidius colemani and one of its secondary parasitoids, Dendrocerus aphidum. Olfactory responses were evaluated for volatile blends emitted by bacteria isolated from diverse sources from the parasitoid's habitat, including aphids, aphid mummies and honeydew, and from the parasitoids themselves. Results revealed that A. colemani showed a wide variation in response to bacterial volatiles, ranging from significant attraction over no response to significant repellence. Our results further showed that the olfactory response of A. colemani to bacterial volatile emissions was different from that of D. aphidum. Gas chromatography-mass spectrometry analysis of the volatile blends revealed that bacterial strains repellent to A. colemani produced significantly higher amounts of esters, organic acids, aromatics and cycloalkanes than attractive strains. Strains repellent to D. aphidum produced significantly higher amounts of alcohols and ketones, whereas the strains attractive to D. aphidum produced higher amounts of the monoterpenes limonene, linalool and geraniol. Overall, our results indicate that bacterial volatiles can have an important impact on insect olfactory responses, and should therefore be considered as an additional, so far often overlooked factor in studying multitrophic interactions between plants and insects. A free Plain Language Summary can be found within the Supporting Information of this article.
  • Chemoecology

    Do plant volatiles confuse rather than guide foraging behavior of the aphid hyperparasitoid Dendrocerus aphidum?

    Jetske G. de Boer, Petra J. Hollander, Divya Jagger, Pim van Sliedregt, Lucia Salis, Martine Kos, Louise E.M. Vet
    Many species of parasitoid wasps use plant volatiles to locate their herbivorous hosts. These volatiles are reliable indicators of host presence when their emission in plants is induced by herbivory. Hyperparasitoids may also use information from lower trophic levels to locate their parasitoid hosts but little is known about the role of volatiles from the plant–host complex in the foraging behavior of hyperparasitoids. Here, we studied how Dendrocerus aphidum (Megaspilidae) responds to plant and host volatiles in a series of experiments. This hyperparasitoid uses aphid mummies as its host and hampers biological control of aphids by parasitoids in greenhouse horticulture. We found that D. aphidum females were strongly attracted to volatiles from mummy-infested sweet pepper plants, but only when clean air was offered as an alternative odor source in the Y-tube olfactometer. Hyperparasitoid females did not have a preference for mummy-infested plants when volatiles from aphid-infested or healthy pepper plants were presented as an alternative. These olfactory responses of D. aphidum were mostly independent of prior experience. Volatiles from the host itself were also highly attractive to D. aphidum, but again hyperparasitoid females only had a preference in the absence of plant volatiles. Our findings suggest that plant volatiles may confuse, rather than guide the foraging behavior of D. aphidum. Mummy hyperparasitoids, such as D. aphidum, can use a wide variety of mummies and are thus extreme generalists at the lower trophic levels, which may explain the limited role of (induced) plant volatiles in their host searching behavior.
  • Scientific Reports

    Molecular quantification of Plasmodium parasite density from the blood retained in used RDTs

    Ailie Robinson, Annette O Busula, Julian K. Muwanguzi, Stephen J Powers, Daniel K Masiga, Teun Bousema, Willem Takken, Jetske G. de Boer, James G Logan, Khalid B Beshir, Colin J Sutherland
  • BioControl

    Effects of temperature and food source on reproduction and longevity of aphid hyperparasitoids of the genera Dendrocerus and Asaphes

    Jetske G. de Boer, Lucia Salis, W. Tollenaar, L.J.M. van Heumen, T.P.M. Costaz, Jeff A. Harvey, Martine Kos, Louise E.M. Vet
    Hyperparasitoids of aphid parasitoids commonly occur in (sweet pepper) greenhouses, and can pose a threat to effective biological control of aphids. Here, we studied life history characteristics of laboratory colonies of Dendrocerus spp. Ratzeburg (Hymenoptera: Megaspilidae) and Asaphes spp. Walker (Pteromalidae) that originated from a commercial sweet pepper greenhouse. We aimed to clarify how these two hyperparasitoid taxa can coexist inside greenhouses. Hyperparasitoids of both taxa have a long lifespan that was extended significantly by food sources that are naturally available in a greenhouse environment, including aphid honeydew and sweet pepper flowers. Differences in sensitivity to decreased or increased temperatures did not appear to explain seasonal patterns in abundance of Dendrocerus spp. and Asaphes spp. in sweet pepper greenhouses. Instead, Dendrocerus spp. may have an advantage early in the season because it thrives on aphid honeydew, while Asaphes spp. may do better later in the season because of its long lifespan and extensive reproductive period.
  • Proceedings of the National Academy of Sciences of the United States of America

    Plasmodium-associated changes in human odor attract mosquitoes

    Ailie Robinson, Annette O Busula, Mirjam A Voets, Khalid B Beshir, John C Caulfield, Stephen J Powers, Niels O. Verhulst, Peter Winskill, Julian K. Muwanguzi, Michael A Birkett, Renate C Smallegange, Daniel K Masiga, W Richard Mukabana, Robert W Sauerwein, Colin J Sutherland, Teun Bousema, John A Pickett, Willem Takken, James G Logan, Jetske G. de Boer

    Malaria parasites (Plasmodium) can change the attractiveness of their vertebrate hosts to Anopheles vectors, leading to a greater number of vector-host contacts and increased transmission. Indeed, naturally Plasmodium-infected children have been shown to attract more mosquitoes than parasite-free children. Here, we demonstrate Plasmodium-induced increases in the attractiveness of skin odor in Kenyan children and reveal quantitative differences in the production of specific odor components in infected vs. parasite-free individuals. We found the aldehydes heptanal, octanal, and nonanal to be produced in greater amounts by infected individuals and detected by mosquito antennae. In behavioral experiments, we demonstrated that these, and other, Plasmodium-induced aldehydes enhanced the attractiveness of a synthetic odor blend mimicking "healthy" human odor. Heptanal alone increased the attractiveness of "parasite-free" natural human odor. Should the increased production of these aldehydes by Plasmodium-infected humans lead to increased mosquito biting in a natural setting, this would likely affect the transmission of malaria.
  • Scientific Reports

    Modulation of plant-mediated interactions between herbivores of different feeding guilds: Effects of parasitism and belowground interactions

    Teresa Vaello, Sandeep J. Sarde, M. Ángeles Marcos-García, Jetske G. de Boer, Ana Pineda
    Herbivory affects subsequent herbivores, mainly regulated by the phytohormones jasmonic (JA) and salicylic acid (SA). Additionally, organisms such as soil microbes belowground or parasitoids that develop inside their herbivorous hosts aboveground, can change plant responses to herbivory. However, it is not yet well known how organisms of trophic levels other than herbivores, below- and above-ground, alter the interactions between insect species sharing a host plant. Here, we investigated whether the parasitoid Aphidius colemani and different soil microbial communities (created through plant-soil feedbacks) affect the JA and SA signalling pathways in response to the aphid Myzus persicae and the thrips Frankliniella occidentalis, as well as subsequent thrips performance. Our results show that the expression of the JA-responsive gene CaPINII in sweet pepper was more suppressed by aphids than by parasitised aphids. However, parasitism did not affect the expression of CaPAL1, a biosynthetic gene of SA. Furthermore, aphid feeding enhanced thrips performance compared with uninfested plants, but this was not observed when aphids were parasitised. Soils where different plant species were previously grown, did not affect plant responses or the interaction between herbivores. Our study shows that members of the third trophic level can modify herbivore interactions by altering plant physiology.
  • Medical and Veterinary Entomology

    Variation in host preferences of malaria mosquitoes is mediated by skin bacterial volatiles

    Annette O Busula, Willem Takken, Jetske G. de Boer, W Richard Mukabana, Niels O. Verhulst

    The host preferences of the anthropophilic mosquito species in the Anopheles gambiae complex (Diptera: Culicidae) are mediated by skin bacterial volatiles. However, it is not known whether these mosquitoes respond differentially to skin bacterial volatiles from non-human host species. In this study, the responses of two malaria mosquito species in the An. gambiae complex, Anopheles gambiae s.s. (hereafter, An. gambiae) and Anopheles arabiensis, with different host preferences, to volatiles released from skin bacteria were tested. Skin bacteria collected from human, cow and chicken skin significantly increased trap catches; traps containing bacteria collected from human skin caught the highest proportions of An. gambiae and An. arabiensis. Traps with bacteria of human origin caught a significantly higher proportion of An. gambiae than of An. arabiensis, whereas bacterial volatiles from the chicken attracted significantly higher numbers of An. arabiensis than of An. gambiae. Additionally, An. gambiae showed a specialized response to volatiles from four specific bacteria, whereas An. arabiensis responded equally to all species of bacteria tested. Skin bacterial volatiles may therefore play important roles in guiding mosquitoes with different host preferences. The identification of these bacterial volatiles can contribute to the development of an odour blend that attracts mosquitoes with different host preferences.
  • PLoS ONE

    Absence of Complementary Sex Determination in the Parasitoid Wasp Genus Asobara (Hymenoptera: Braconidae)

    Wen Juan Ma, Bram Kuijper, Jetske G. de Boer, Louis van de Zande, Leo W. Beukeboom, Bregje Wertheim, Bart A. Pannebakker

    An attractive way to improve our understanding of sex determination evolution is to study the underlying mechanisms in closely related species and in a phylogenetic perspective. Hymenopterans are well suited owing to the diverse sex determination mechanisms, including different types of Complementary Sex Determination (CSD) and maternal control sex determination. We investigated different types of CSD in four species within the braconid wasp genus Asobara that exhibit diverse life-history traits. Nine to thirteen generations of inbreeding were monitored for diploid male production, brood size, offspring sex ratio, and pupal mortality as indicators for CSD. In addition, simulation models were developed to compare these observations to predicted patterns for multilocus CSD with up to ten loci. The inbreeding regime did not result in diploid male production, decreased brood sizes, substantially increased offspring sex ratios nor in increased pupal mortality. The simulations further allowed us to reject CSD with up to ten loci, which is a strong refutation of the multilocus CSD model. We discuss how the absence of CSD can be reconciled with the variation in life-history traits among Asobara species, and the ramifications for the phylogenetic distribution of sex determination mechanisms in the Hymenoptera.
  • Evolutionary Applications

    Sex determination meltdown upon biological control introduction of the parasitoid Cotesia rubecula?

    Jetske G. de Boer, Bram Kuijper, George E. Heimpel, Leo W. Beukeboom

    Natural enemies may go through genetic bottlenecks during the process of biological control introductions. Such bottlenecks are expected to be particularly detrimental in parasitoid Hymenoptera that exhibit complementary sex determination (CSD). CSD is associated with a severe form of inbreeding depression because homozygosity at one or multiple sex loci leads to the production of diploid males that are typically unviable or sterile. We observed that diploid males occur at a relatively high rate (8-13% of diploid adults) in a field population of Cotesia rubecula in Minnesota, USA, where this parasitoid was introduced for biological control of the cabbage white Pieris rapae. However, our laboratory crosses suggest two-locus CSD in a native Dutch population of C. rubecula and moderately high diploid males survival (approximately 70%), a scenario expected to produce low proportions of diploid males. We also show that courtship behavior of diploid males is similar to that of haploid males, but females mated to diploid males produce only very few daughters that are triploid. We use our laboratory data to estimate sex allele diversity in the field population of C. rubecula and discuss the possibility of a sex determination meltdown from two-locus CSD to effective single-locus CSD during or after introduction.

Projects & collaborations


  • Maasheggen: unique field laboratory for agrobiodiversity

    Project 2019–Present
    The Maasheggen area is a unique cultivated landscape in the Netherlands (near Boxmeer, province Noord-Brabant) and has been designated as a UNESCO biosphere reserve ( Its mosaic of hedgerows, small arable fields and meadows make this a very interesting area to study the effects of land use and landscape elements on functional biodiversity and ecosystem services.
    Maasheggen insect sampling
  • Smart natural enemies for sustainable pest control

    Project 2021–2024
    Parasitoids are key natural enemies that contribute to biological control of economically important pests in both agricultural and natural ecosystems. They are however not always efficient in finding the pest insect in the greenhouse because the (mass-)rearing conditions differ from the greenhouse environment in which they are released. This reduces parasitoid motivation and efficiency to search for herbivore insect pests.
    Cut roses in greenhouse
  • Lectoraat Ecologisch Wijs: Insecten & Maatschappij

    Project 2020–2024
    Eikenprocessierups, buxusmot en mug. Er zijn genoeg plagen die ons de kriebels kunnen bezorgen. Maar veel meer insectensoorten zijn juist onmisbaar en verdienen aandacht omdat het slecht met ze gaat. Die twee uitersten hebben meer met elkaar te maken dan je denkt, stelt Jetske de Boer. Sinds 2020 werkt zij als lector Insecten & Maatschappij bij Aeres Hogeschool Wageningen én het Nederlands Instituut voor Ecologie (NIOO-KNAW) aan praktische oplossingen.
    Blije steen: Mieren