Wolbachia-infected Trichogramma dendrolimi is outcompeted by its uninfected counterpart in superparasitism but does not have developmental delay.

Abstract

Wolbachia infection increases the superparasitism frequency of Trichogramma females and provides an opportunity for horizontal intraspecific transmission. However, superparasitism may lead to interstrain competition between Wolbachia-infected Trichogramma offspring and their uninfected counterparts. This study investigated the outcome of interstrain intrinsic competition between Wolbachia-infected thelytokous strain (W) and uninfected bisexual strain (B) of Trichogramma dendrolimi. To determine the developmental rate of both strains, the sizes of immature stages of T. dendrolimi offspring at different times after parasitisation were measured in single parasitism and superparasitism conditions. The results reflect increased superparasitism by Wolbachia-infected females compared with uninfected females. Trichogramma females did not discriminate between host eggs previously parasitised by either B or W females. When the first oviposition was performed by B females, the B offspring outcompeted W offspring deposited later. Although when W offspring was deposited 8h earlier than the B offspring, it gained no advantage over B offspring. Regardless of parasitism conditions, differences in the development rate between W and B offspring were not significant. The results reconfirmed that W females presented a higher tendency for superparasitism than B females, and showed that B offspring outcompeted W offspring even when the latter was deposited 8h earlier. The inferiority of Wolbachia-infected Trichogramma compared with their uninfected counterparts is not due to the developmental delay. This study provides insights into the effects of intrinsic competition on the control efficacy of Wolbachia-infected Trichogramma against pests in biological control programs. © 2022 Society of Chemical Industry.