A Comparative Functional Approach to the Host Detection Behaviour of Parasitic Wasps. 1. A Qualitative Study on Eucoilidae and Alysiinae

We studied host detection behaviour in Alysiinae (Braconidae; Ichneumonoidea) and Eucoilidae (Cynipoidea), the larvae of which are endoparasitoids of fly larvae and in- vestigated whether this behaviour is determined by their descent or can be considered an adaptation to different environments. We compared the searching behaviour of fe- males of 32 alysiine and 25 eucoilid species from a variety of microhabitats and from different dipteran hosts by using qualitative behavioural variables. Three main modes of searching were detected: vibrotaxis, ovipositor searching and antennal searching, and the species could be classified according to the role these different modes play in the detection of host larvae. The searching modes are largely dependent upon the taxonomic position of the species. In most cases species belonging to one genus show a similar behaviour pattern. However, we also encountered examples of radiation; closely related species that search differently. The function of the three searching modes has not been elucidated so far. Therefore we cannot say that similar searching modes in unrelated species are examples of adaptive convergence. Especially in Drosophila parasitoids we encountered great differences in searching behaviour be- tween different species living in the same microhabitat. We believe differences at all levels of searching, including host detection behaviour may contribute to niche segre- gation and create possibilites for different parasitoid species to coexist in the same microhabitat, even when they attack the same host species

Optimal Resource Allocation to Survival and Reproduction in Parasitic Wasps Foraging in Fragmented Habitats

Expansion and intensification of human land use represents the major cause of habitat fragmentation. Such fragmentation can have dramatic consequences on species richness and trophic interactions within food webs. Although the associated ecological consequences have been studied by several authors, the evolutionary effects on interacting species have received little research attention. Using a genetic algorithm, we quantified how habitat fragmentation and environmental variability affect the optimal reproductive strategies of parasitic wasps foraging for hosts. As observed in real animal species, the model is based on the existence of a negative trade-off between survival and reproduction resulting from competitive allocation of resources to either somatic maintenance or egg production. We also asked to what degree plasticity along this trade-off would be optimal, when plasticity is costly. We found that habitat fragmentation can indeed have strong effects on the reproductive strategies adopted by parasitoids. With increasing habitat fragmentation animals should invest in greater longevity with lower fecundity; yet, especially in unpredictable environments, some level of phenotypic plasticity should be selected for. Other consequences in terms of learning ability of foraging animals were also observed. The evolutionary consequences of these results are discussed

Habitat complexity reduces parasitoid foraging efficiency, but does not prevent orientation towards learned host plant odours

It is well known that many parasitic wasps use herbivore-induced plant odours (HIPVs) to locate their inconspicuous host insects, and are often able to distinguish between slight differences in plant odour composition. However, few studies have examined parasitoid foraging behaviour under (semi-)field conditions. In nature, food plants of parasitoid hosts are often embedded in non-host-plant assemblages that confer both structural and chemical complexity. By releasing both naïve and experienced Cotesia glomerata females in outdoor tents, we studied how natural vegetation surrounding Pieris brassicae-infested Sinapis arvensis and Barbarea vulgaris plants influences their foraging efficiency as well as their ability to specifically orient towards the HIPVs of the host plant species on which they previously had a positive oviposition experience. Natural background vegetation reduced the host-encounter rate of naïve C. glomerata females by 47 %. While associative learning of host plant HIPVs 1 day prior to foraging caused a 28 % increase in the overall foraging efficiency of C. glomerata, it did not reduce the negative influence of natural background vegetation. At the same time, however, females foraging in natural vegetation attacked more host patches on host-plant species on which they previously had a positive oviposition experience. We conclude that, even though the presence of natural vegetation reduces the foraging efficiency of C. glomerata, it does not prevent experienced female wasps from specifically orienting towards the host-plant species from which they had learned the HIPVs