Possible effects of inter-specific competition on the coexistence of two parasitoid species:Trichogramma brassicaeBezdenko andChelonus oculator(F.) (Hymenoptera: Trichogrammatidae, Braconidae)

Abstract

Insect parasitoids have been widely studied, particularly due to their ecological implications through the study of the special relationships observed among this kind of species, as well as to their expression in mathematical models. However, there are still scarce studies on parasitoid relationships and their expression in more realistic mathematical models. The present work is aimed at deepening into competition relationships among parasitoids. Bearing this purpose in mind, the system shaped by two parasitoids was chosen: Trichogramma brassicae (idiobiont egg parasitoid) and Chelonus oculator (koinobiont egg-larval parasitoid). Both species compete against each other for the same host species (Lepidoptera). The results obtained in the laboratory point out that T. brassicae may be considered a better competitor than Ch. oculator. This is the result of the extrinsic competition due to the substances injected by the female during parasitization. However, our results show this classification into better and worse competitors inaccurate. Thus, these interspecific competition influences are detrimental to both parasitoid species. This is the first time that the effect of this competition is mentioned regarding parasitoid functional response. Our results and their ecological implications are reported and discussed.