Complex interactions in biological control

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Biological control is the use of natural enemies (pathogens, parasites and predators) to suppress pest populations. It is a viable and sustainable alternative to synthetic pesticides. However, numerous biotic and abiotic factors may influence the effectiveness of biocontrol agents. My research is aimed at identifying some of the governing ecological principles and mechanisms of multispecies interactions within arthropod communities. This research is both essential and timely, for an increasing number of biocontrol agents are available in agriculture. Furthermore, climate change may compromise biological control. Rising temperatures and increasing extreme climatic events not only affect species performance, but also species interactions. Climate change is expected to directly affect biological control by modifying (i) the relative metabolic rate and associated processes (e.g., development, foraging, reproduction) between pest and natural enemies, and (ii) both the spatial and temporal synchrony of biocontrol agents and pests. Using different predator-parasitoid models, as well as a large data set on thermal responses of biological control agents my students and I have recently collected, we propose to examine (i) how temperature-mediated metabolic changes, especially at low and high temperatures, influence the foraging behaviour and reproduction of natural enemies and thereby determine their top-down effect on pest populations, and (ii) how potential phenological mismatching between pests and their natural enemies can limit biological control - through the use of an index that identifies prey/host-predator/parasite relationships that are susceptible to be disrupted by climate change. A second axis of my program relates to strategies evolved by parasitic wasps to exploit their host, more specifically their ability to manipulate host behaviour. I wish to study, from proximate and ultimate mechanisms to ecological consequences, a type of host manipulation that has been largely unexplored: the bodyguard manipulation. We observed that a parasitic wasp has the capacity to transform its ladybird host into a bodyguard while developing within its cocoon, which results in a significant reduction in predation on the developing parasite. Furthermore, and unexpectedly, ladybirds may recover from parasitism. I plan to first quantify different aspects of the natural history of the parasitic wasp by conducting field work to improve our understanding of its host specificity, seasonal ecology and role in agroecosystems. Next, I wish to answer two important questions on the ecological attributes of parasitized ladybirds. First, to what extent does parasitism impair ladybird performance? Second, from an applied perspective, do parasitized ladybirds have intrinsically the same capacity to regulate aphid populations as unparasitized conspecifics under field conditions?