PhD Defense - David MURU

Abstract :

Biological control (or biocontrol) is the use of living organisms to suppress the population density or impact of a specific pest organism, making it less abundant or less damaging than it would otherwise be. The biological control agent may directly or indirectly interact with more than just the target pest and vice versa. Therefore, monitoring its populations, in conjunction to other ecological factors, may allow to confirm or discard ecology theories or unveil brand new interactions with both abiotic and biotic facets of the recipient ecosystem. Moreover, the methodological aspects of the post release monitoring phase and those of ecological experimentations sometimes do share similarities. In this work I explore how both disciplines -are reconciled and how the resulting data from biocontrol could be optimized for its use in ecology. I use data from biological control programs to address questions related to invasion dynamics, community ecology and landscape ecology. In chapter 1, I detail the case studies: (i) the introduction of the parasitoid Torymus sinensis (Hymenoptera: Torymidae) against the Asian chestnut gall wasp Dryocosmus kuriphilus (Hymenoptera: Cynipidae) ; (ii) the introduction of the ectoparasitoid Mastrus ridens (Hymenoptera: Ichneumonidae) against the codling moth Cydia pomonella (Lepidoptera: Tortricidae) ; (iii) a nation-wide survey of Trichogramma species in France in order to characterize the ecological ranges of each species; (iv) the description of egg parasitoid species associated with Iphiclides podalirius (Lepidoptera: Papilionidae) at a fine temporal scale. Chapter 2 is focused on understanding the dispersal of T. sinensis at the scale of several chestnut producing areas. In this chapter, I use monitoring data from release sites to fit a growth model for populations of T. sinensis in order to infer the time since colonization in naturally colonized sites. In chapter 3 I investigate the impacts of the successful control of D. kuriphilus by T. sinensis on the structure of native parasitoid community that recently became associated with the pest. Chapter 4 is focused on cases where scientific valorization ranges from a complete failure (primo-introduction of M. ridens), the diffusion of naturalist knowledge (survey of I. podalirius and related oophagous parasitoids) and/or the identification of some patterns using specific statistics (national survey of Trichogramma species). Finally, by compiling knowledge from the extensive literature on biological control and field experience I then discuss on the potentials and limits of biological control programs for experimental ecology. I conclude that although biological control gives an ecological context to experimentation by allowing to manipulate a wide variety of factors, the context and the organisms at play may not be compatible with any ecological issue. For example, the obvious parallel between classical biological control and invasion biology makes the former extremely useful to study ecological processes that drive the success of invasions. This in turn could yield knowledge that may have implication in other disciplines such as the preservation of endangered species. However, factors like the low detectability of a biological control agent at low densities (coupled with varying sensibility of monitoring methods) may render the study of early stages dynamics and interactions too much of a daunting endeavor. Key words : Biological control, Experimental ecology, Community ecology, Population dynamics, Classical biocontrol. 

Jury :

Thierry Hance : President du jury et rapporteurHélène Delatte : rapportriceLise Roy : examinatriceElodie Vercken : directrice de thèseNicolas Ris : co-directeur de thèse