Trichogramma species (Hymenoptera: Trichogrammatidae) are haplo-diploid egg parasitoids that are frequently used as biological control agents against lepidopteran pests. These wasps display two reproductive modes, including arrhenotoky (bisexuality) and thelytoky (unisexuality). Thelytokous forms are often associated with the presence of endosymbiotic Wolbachia bacteria. The use of thelytokous wasps has long been considered as a way to enhance the efficacy of biological control. The present study investigates the potential of a thelytokous Wolbachia-infected and an arrhenotokous uninfected Trichogramma brassicae Bezdenko strain as inundative biocontrol agents by evaluating their functional response towards different egg densities of the factitious host, the Angoumois grain moth, Sitotroga cerealella (Olivier) (Lepidoptera: Gelechiidae). The results revealed a type II functional response for both strains in which parasitism efficiency decreases with host egg density because of an increasing host handling time. A model with an indicator variable was used to compare the parameters of Holling's disc equation in different data sets. It was demonstrated that the two strains did not differ in host attack rate. However, the Wolbachia-infected strain did have an increased host handling time when compared to the bisexual strain. Some applied aspects of the findings are discussed.
Various physiological effects of Wolbachia infection have been reported in invertebrates, but the impact of this infection on behavior and the consequences of these behavioral modifications on fitness have rarely been studied. Here, we investigate the effect of Wolbachia infection on the estimation of host nutritive resource quality in a parasitoid wasp. We compare decision-making in uninfected and Wolbachia-infected strains of Trichogramma brassicae Bezdenko (Hymenoptera: Trichogrammatidae) on patches containing either fresh or old host eggs. For both strains, fresh eggs were better hosts than older eggs, but the difference was smaller for the infected strain than for the uninfected strain. Oviposition behavior of uninfected wasps followed the predictions of optimal foraging theory. They behaved differently toward high-vs. low-quality hosts, with more hosts visited and more ovipositions, fewer high-quality hosts used for feeding or superparasitism, and a sex ratio that was more biased toward females in patches containing high-quality hosts than in patches containing low-quality ones. Uninfected wasps also displayed shorter acceptance and rejection times in high-quality hosts than in hosts of lower quality. In contrast, infected wasps were less efficient in evaluating the nutritive quality of the host (fresh vs. old eggs) and had a reduced ability to discriminate between unparasitized and parasitized hosts. Furthermore, they needed more energy and therefore engaged in host feeding more often. This study highlights possible decision-making manipulation by Wolbachia, and we discuss its consequences for Wolbachia fitness.
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