Papers by Joan Van Baaren
Annual Review of Entomology, 2007
Parasitoids depend on a series of adaptations to the ecology and physiology of their hosts and ho... more Parasitoids depend on a series of adaptations to the ecology and physiology of their hosts and host plants for survival and are thus likely highly susceptible to changes in environmental conditions. We analyze the effects of global warming and extreme temperatures on the life-history traits of parasitoids and interactions with their hosts. Adaptations of parasitoids to low temperatures are similar to those of most ectotherms, but these adaptations are constrained by the responses of their hosts. Life-history traits are affected by cold exposure, and extreme temperatures can reduce endosymbiont populations inside a parasitoid, eventually eliminating populations of endosymbionts that are susceptible to high temperatures. In several cases, divergences between the thermal preferences of the host and those of the parasitoid lead to a disruption of the temporal or geographical synchronization, increasing the risk of host outbreaks. A careful analysis on how host-parasitoid systems react to changes in temperature is needed so that researchers may predict and manage the consequences of global change at the ecosystem level.
Journal of Insect Physiology, 2012
Metabolic rate, a physiological trait closely related to fitness traits, is expected to evolve in... more Metabolic rate, a physiological trait closely related to fitness traits, is expected to evolve in response to two main environmental variables: (1) climate, low metabolic rates being found in dry and hot regions when comparing populations originating from different climates in a common garden experiment and (2) resource limitations, low metabolic rates being selected when resources are limited. The main goal of this study was to investigate if differences in intrinsic resource limitations may have disrupted the expected evolution of metabolic rate in response to climate in a parasitic wasp. We compared CO(2) production of females from 4 populations of a Drosophila parasitoid, Leptopilina boulardi, as an estimate of their metabolic rate. Two populations from a hot and dry area able to synthesise lipids de novo at adult stage were compared with two populations originating from a mild and humid climate where no lipid accumulation during adult life was observed. These last females are thus more limited in lipids than the first ones. We observed that a high metabolic rate has been selected in hot and dry environments, contrarily to the results of a great majority of studies. We suggest that lipogenesis occurring there may have allowed the selection of a higher metabolic rate, as females are less limited in energetic resources than females from the mild environment. A high metabolic rate may have been selected there as it partly compensates for the long distances that females have to cross to find laying opportunities in distant orchards. We suggest that intrinsic resources should be integrated when investigating geographical variations in metabolism as this factor may disrupt evolution in response to climate.
BioControl, 2012
Cold storage of insect parasitoids is currently used before mass release in the field in biologic... more Cold storage of insect parasitoids is currently used before mass release in the field in biological control programmes. The physiological consequences of constant cold storage are known in various species of parasitic wasps, but there are few reports on the behaviour of survivors and even fewer reports where both sexes were tested. In this study, we observed the consequences of a long storage of Aphidius rhopalosiphi De Stephani Perez (Hymenoptera: Braconidae), a parasitoid of the cereal aphid Sitobion avenae Fabricius (Hemiptera: Aphididae), at low temperature on some key behavioural decisions that both sexes will make when released in the field. Males are less tolerant than females and both sexes suffer from a long exposure (28 days or more) at 4°C during the pupal stage: alteration of olfactory responses, decrease in mating capacity and decrease in the efficiency of patch exploitation by females.
Bulletin of Entomological Research, 2009
Three related Aphidius parasitoid species share the same host, the grain aphid Sitobion avenae. A... more Three related Aphidius parasitoid species share the same host, the grain aphid Sitobion avenae. Among this parasitoid community, Aphidius rhopalosiphi is the most abundant species in the field. Both the interspecific host discrimination of A. rhopalosiphi towards hosts parasitized by the two other species (i.e. A. avenae and A. ervi) and the interspecific host discrimination of the two other species towards hosts parasitized by A. rhopalosiphi were studied here. Results showed that females of A. rhopalosiphi and A. avenae both discriminated between unparasitized hosts and hosts parasitized by the other species. This discrimination occurred only after ovipositor insertion, suggesting the perception of an internal marker of parasitism. Likewise, females of A. rhopalosiphi and A. ervi were able to discriminate between unparasitized hosts and hosts parasitized by the other species. However, in this combination of species, recognition of parasitized hosts occurred before ovipositor insertion, through an antennal perception, suggesting the presence an external cue indicating parasitism. Hence, interspecific host discrimination in the three Aphidius species is based on internal or external cues, which are used either alone or together. Our results showed that the cues used for interspecific host discrimination depend on the specific identity of the interaction. These differences seemed strongly linked to the way the different species respond to defensive behaviours of their aphid hosts. Results are discussed in the context of optimal foraging and possible consequences for community structure.
Entomologia Experimentalis et Applicata, 2013
Journal of Theoretical Biology, 2012
Temperature increase can affect physiological and behavioural constraints. Here, we use a stochas... more Temperature increase can affect physiological and behavioural constraints. Here, we use a stochastic dynamic modelling approach to predict changes in physiological adaptations and behaviour in response to temperature increase of pro-ovigenic parasitoids (i.e., parasitoids that mature all of their eggs before emergence). Adults of most species of parasitoids, are not capable of de novo lipogenesis. The allocation of lipids accumulated during the larval stage determines adult lifespan and fecundity. In females, lipids can be allocated either to egg production or to adult lipid reserves leading to a trade-off between fecundity and lifespan.
Learning of olfactory and gustatory cues occurs throughout the adult stage of parasitoids, partic... more Learning of olfactory and gustatory cues occurs throughout the adult stage of parasitoids, particularly during host location and patch exploitation. A loss of learning capacities could affect both the whole hostparasitoid system and the wasps' reproductive success. We analysed the effect of low-temperature exposure on learning, patch exploitation strategies and patch-leaving rules used by Anaphes victus (Hymenoptera: Mymaridae). Females were stored 0, 3, 6 and 12 weeks at 4 C at the second larval instar. After emergence, females were offered three successive patches containing 16 hosts, of which 0, 50 and 100%, respectively, were parasitized, and their foraging behaviours were recorded. Cold-exposed females oviposited fewer eggs, seemed less able to learn external marks (or did not use their learning capacities), oviposited more in already parasitized hosts and used different patch-leaving rules to control females. The degree of the change in behaviour was positively correlated with the duration of cold exposure. Low-temperature exposure thus affected the reproductive success, expression of learning, host discrimination ability and patch-leaving decision rules of the parasitic wasps. We discuss the implications of these effects on the pattern of patch exploitation for biological control and field situations.
Coexistence of species sharing the same resources is often possible if species are phylogenetical... more Coexistence of species sharing the same resources is often possible if species are phylogenetically divergent in resource acquisition and allocation traits, decreasing competition between them. Developmental and life-history traits related to resource use are influenced by environmental conditions such as temperature, but thermal trait responses may differ among species. An increase in ambient temperature may, therefore, affect trait divergence within a community, and potentially species coexistence. Parasitoids are interesting models to test this hypothesis, because multiple species commonly attack the same host, and employ divergent larval and adult host use strategies. In particular, development mode (arrested or continued host growth following parasitism) has been recognized as a major organiser of parasitoid life histories. Here, we used a comparative trait-based approach to determine thermal responses of development time, body mass, egg load, metabolic rate and energy use of the coexisting Drosophila parasitoids Asobara tabida, Leptopilina heterotoma, Trichopria drosophilae and Spalangia erythromera.W e compared trait values between species and development modes, and calculated trait divergence in response to temperature, using functional diversity indices. Parasitoids differed in their thermal response for dry mass, metabolic rate and lipid use throughout adult life, but only teneral lipid reserves and egg load were affected by developmental mode. Species-specific trait responses to temperature were probably determined by their adaptations in resource use (e.g. lipogenesis or ectoparasitism). Overall, trait values of parasitoid species converged at the higher temperature. Our results suggest that local effects of warming could affect host resource partitioning by reducing trait diversity in communities.
Environmental pollution (Barking, Essex : 1987), Jan 23, 2015
Organisms are regularly subjected to abiotic stressors related to increasing anthropogenic activi... more Organisms are regularly subjected to abiotic stressors related to increasing anthropogenic activities, including chemicals and climatic changes that induce major stresses. Based on various key taxa involved in ecosystem functioning (photosynthetic microorganisms, plants, invertebrates), we review how organisms respond and adapt to chemical- and temperature-induced stresses from molecular to population level. Using field-realistic studies, our integrative analysis aims to compare i) how molecular and physiological mechanisms related to protection, repair and energy allocation can impact life history traits of stressed organisms, and ii) to what extent trait responses influence individual and population responses. Common response mechanisms are evident at molecular and cellular scales but become rather difficult to define at higher levels due to evolutionary distance and environmental complexity. We provide new insights into the understanding of the impact of molecular and cellular re...
In stressful environments, two main hypotheses have been proposed to explain the consequences of ... more In stressful environments, two main hypotheses have been proposed to explain the consequences of body size: (1) the absolute energy demand hypothesis (AED), which predicts that larger individuals are at a disadvantage under stressful conditions; (2) the relative effi ciency hypothesis (RE), which predicts the reverse. We compared the eff ects of cold stress on diff erent fi tness traits of large and small individuals of the parasitoid wasp Aphidius ervi (Hymenoptera: Aphidiinae). For that, we exposed nymphs of this wasp to 5 treatment conditions as follows (control at 20 ° C; 7C1 and 7C2: constant cold temperature of 7 ° C for 1 and 2 weeks respectively; 4C1 and 4C2: constant cold temperature of 4 ° C for 1 and 2 weeks respectively).
The nature of early relationships between mother and nymphs and among siblings was compared in fo... more The nature of early relationships between mother and nymphs and among siblings was compared in four cockroach species belonging to the same ovoviviparous family (Zetoborinae) in order to characterise the behavioural interactions favouring dispersal or maintenance of the group of neonates. Behavioural interactions between mothers and their new-born nymphs and between two sibling neonates were video recorded and analysed with flow charts on factorial maps. In the solitary species Thanatophyllum akinetum, nymphs dispersed a few hours after birth without aggressiveness between siblings or between mother and offspring. In contrast females of Schultesia lampyridiformis displayed a behaviour never previously observed in cockroaches: aggression towards their own neonate nymphs, which could contribute to their dispersal. In Phortioeca nimbata and Lanxoblatta emarginata, nymphs stayed with their mother for 10 days, but social interactions differed between the two species: P. nimbata mothers actively searched for their nymphs, this behaviour being favoured by an active search for mutual contact by the nymphs themselves, while L. emarginata nymphs sought more actively the proximity of their mother but less contact between themselves. Thus, different species of Zetoborinae presented two types of dispersal of the young and two types of maintenance of the birth group, both achieved by specific behavioural interactions. The relevance of behavioural interactions for the characterisation of early gregarism and parental care is discussed.
Insects observed in groups in nature may be gathered either by attractants from the environment o... more Insects observed in groups in nature may be gathered either by attractants from the environment or by conspecifics. Field distribution data alone are thus insufficient to assess congregation by conspecifics and complementary laboratory tests of spacing patterns are required. Such tests were performed in four species of Zetoborinae (Insecta, Blattaria), for which field studies showed differences in spatial distribution (Schultesia lampyridiformis Roth, Phortioeca nimbata Burmeister, Lanxoblatta emarginata Burmeister and Thanatophyllum akinetum Grandcolas). Gregariousness, mobility, and sticking to shelters were compared between these four species. Tests were performed on pairs of adults of the same sex and opposite sexes, and also on first instar larvae, either in isolation or in groups of two and four individuals. In S. lampyridiformis, adults were strongly gregarious, whereas larvae dispersed early after birth and were very mobile during the first instar. In P. nimbata, larvae and adults were gregarious, while in L. emarginata larvae were weakly gregarious, and gregariousness decreased when density increased. Adults of L. emarginata seemed to be indifferent to each other. Larvae and adults of T. akinetum were solitary and they actively dispersed. The varying levels of gregariousness among species are discussed according to the known ecological habits in Zetoborinae.
PloS one, 2014
Traits of physiological thermotolerance are commonly measured in the laboratory as predictors of ... more Traits of physiological thermotolerance are commonly measured in the laboratory as predictors of the field success of ectotherms at unfavourable temperatures (e.g. during harsh winters, heatwaves, or under conditions of predicted global warming). Due to being more complicated to measure, behavioural thermoregulation is less commonly studied, although both physiology and behaviour interact to explain the survival of ectotherms. The aphids Metopolophium dirhodum, Rhopalosiphum padi and Sitobion avenae are commercially important pests of temperate cereal crops. Although coexisting, these species markedly differ in winter success, with R. padi being the most abundant species during cold winters, followed by S. avenae and lastly M. dirhodum. To better understand the thermal physiology and behavioural factors contributing to differential winter success, the lethal temperature (physiological thermotolerance) and the behaviour of aphids in a declining temperature regime (behavioural thermot...
Zoomorphology, 1997
Anaphes victus and A. listronoti are two closely related species, respectively solitary and grega... more Anaphes victus and A. listronoti are two closely related species, respectively solitary and gregarious parasitoids of eggs of the carrot weevil Listronotus oregonensis (Coleoptera, Curculionidae). Both species are sympatric, and the regulation of super-and multiparasitism that occurs regularly in this host is done by larval fights between the mymariform first instar larvae. The morphology of both male and female first instar larvae of A. victus and A. listronoti is described using scanning electron microscopy. Both species have first instar larvae of the mymariform type and present sexual dimorphism. The main difference between the two species is that larvae of A. victus are clearly segmented while larvae of A. listronoti show no visible segmentation. Male larvae of both species have two types of perioral hooks, longer and less dense dorsal setae than females and developed undertail spines. Female larvae of both species have short abdominal setae. These morphological differences are discussed in the context of intra-and interspecific larval competition.& b d y :
Oikos, 2012
In stressful environments, two main hypotheses have been proposed to explain the consequences of ... more In stressful environments, two main hypotheses have been proposed to explain the consequences of body size: (1) the absolute energy demand hypothesis (AED), which predicts that larger individuals are at a disadvantage under stressful conditions; (2) the relative effi ciency hypothesis (RE), which predicts the reverse. We compared the eff ects of cold stress on diff erent fi tness traits of large and small individuals of the parasitoid wasp Aphidius ervi (Hymenoptera: Aphidiinae). For that, we exposed nymphs of this wasp to 5 treatment conditions as follows (control at 20 ° C; 7C1 and 7C2: constant cold temperature of 7 ° C for 1 and 2 weeks respectively; 4C1 and 4C2: constant cold temperature of 4 ° C for 1 and 2 weeks respectively).
Evolutionary Ecology, 2012
Species belonging to the same guild (i.e. sharing the same resources) can reduce the negative eff... more Species belonging to the same guild (i.e. sharing the same resources) can reduce the negative effects of resource competition through niche partitioning. Coexisting species may differ in their resource exploitation and in the associated allocation of nutrients, depending on their resource niche. Trade-offs in nutrient allocation, such as between reproduction and survival, or between early and late reproduction, are moderated by the abundance and distribution of resources. In this study we investigate differences in larval resource exploitation and adult reproductive strategy of two sympatric aphid parasitoids sharing a common host. The habitat specialist Aphidius rhopalosiphi and the generalist Aphidius avenae occur in cereal crops of Western Europe, where both species attack the major host resource: the grain aphid Sitobion avenae. For this purpose, we measured their acquisition of capital lipid resources, their age-specific fecundity and reproductive effort, their life span and their metabolic rate. We found that these species do not differ neither in larval lipid accumulation nor in the number of eggs at emergence and the timing of egg production, but diverge in other adult reproductive strategies. The rate of adult egg production was higher in A. rhopalosiphi than A. avenae, but at the expense of producing smaller eggs. Throughout adult life, reproductive effort was higher in A. avenae, perhaps facilitated by its higher metabolic rate than A. rhopalosiphi. The divergence between species in life history syndromes likely reflects their adaptations to their resource niche. A high egg production probably allows the specialist A. rhopalosiphi to exploit more S. avenae individuals in cereal crops, while the generalist A. avenae because of its variety of hosts, maximizes the investment per egg but at the expense of a lower lifespan. Our results suggest that differential resource allocation may be a more common pattern that promotes coexistence of species within a guild.
Entomologia Experimentalis et Applicata, 2013
Organisms can either evade winter's unfavourable conditions by migrating or diapausing, or endure... more Organisms can either evade winter's unfavourable conditions by migrating or diapausing, or endure them and maintain their activities. When it comes to foraging during winter, a period of scarce resources, there is strong selective pressure on resource exploitation strategy. Generalist parasitoids are particularly affected by this environmental constraint, as their fitness is deeply linked to the profitability of the available hosts. In this study, we considered a cereal aphid-parasitoid system and investigated (1) the host-parasitoid community structure, host availability, and parasitism rate in winter, (2) the influence of host quality in terms of species and instars on the fitness of the aphid parasitoid Aphidius rhopalosiphi De Stefani-Perez (Hymenoptera: Braconidae: Aphidiinae), and (3) whether there is a detectable impact of host fidelity on parasitism success of this parasitoid species. Host density was low during winter and the aphid community consisted of the species Rhopalosiphum padi L. and Sitobion avenae Fabricius (both Hemiptera: Aphididae), both parasitized by A. rhopalosiphi at non-negligible rates. Aphidius rhopalosiphi produced more offspring when parasitizing R. padi compared with S. avenae, whereas bigger offspring were produced when parasitizing S. avenae. Although aphid adults and old larvae were significantly larger hosts than young larvae, the latter resulted in higher emergence rates and larger parasitoids. No impact of host fidelity on emergence rates or offspring size was detected. This study provides some evidence that winter A. rhopalosiphi populations are able to take advantage of an array of host types that vary in profitability, indicating that host selectivity may drop under winter's unfavourable conditions.
Ecological Modelling, 2011
Adult parasitoid females lay their eggs in or on host insects. Most species are incapable of de n... more Adult parasitoid females lay their eggs in or on host insects. Most species are incapable of de novo lipogenesis as adults, and lipids accumulated during the larval stage are allocated either to egg production or to adult survival. Lipid consumption increases with distance covered by the parasitoids and thus with the distance between available hosts within a habitat. Temperature should affect parasitoid fitness because it changes the constraint imposed by a limited reserve of lipids and because it influences behaviour. Climate change involves both an increase in average temperature and an increased frequency of extreme weather such as heat waves. We investigated how the predicted increase of temperature will affect parasitoid fitness and how this depends on habitat parameters (spatial distribution of hosts and lipid cost of habitat exploitation). We studied optimal behaviour and calculated fitness at different temperatures and in different habitats using a stochastic dynamic programming model for pro-ovigenic parasitoids (which mature all their eggs before becoming adult). We show that an increase in temperature decreases fitness of parasitoids adapted to lower temperatures. This decrease in fitness depends on habitat quality. In field conditions (assuming small costs of intra-patch foraging), the loss of fitness should be larger in habitats with high inter-patch distance and in habitats with a more aggregated distribution of hosts. The foraging behaviour of parasitoids is also affected; at higher temperature we show that intra-patch foraging becomes less efficient, and patch residence times are longer.
Ecological Entomology, 2008
1. In solitary parasitoids, several species can exploit the same host patch and competition could... more 1. In solitary parasitoids, several species can exploit the same host patch and competition could potentially be a strong selective agent as only one individual can emerge from a host. In cereal crops, Aphidius rhopalosiphi and A. ervi share the grain aphid Sitobion avenae as host.
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Papers by Joan Van Baaren