Wolbachia effect on olfactory responses and parasitism rate of Trichogramma brassicae in laboratory conditions

Trichogramma wasps (Hym., Trichogrammatidae) are frequently used as egg parasitoid and biological control agent of lepidopteran pests. These haplodiploid wasps display two reproductive modes, including thelytoky and arrhenotoky. The thelytoky (unisexuality) are often associated with the presence of endosymbiotic Wolbachia bacteria (α-proteobacteria). The use of thelytokous parasitoids has long been considered as a way to enhance the biocontrol efficacy. In this study a series of experiments were conducted to compare the behavioral aspects, dispersal potential and parasitism of thelytokous (BW+) and bisexual (B) Trichogramma brassicae strains (Baboulsar ecotype) at 25◦C in laboratory conditions. By using Y-tube olfactometer, it was observed that the Wolbachia infection in the Baboulsar strain (mixed population) neither affected the wasp's response to volatile odors of honey water solution and factitious host eggs nor did it interfere with female wasp's sex pheromone emission. Greenhouse release tests on corn plants, resulted in non significant differences between the strains taking the number of parasitized eggs per one female wasp into consideration. However, based on releasing 100 wasps (male and female in the case of bisexual), the number of egg masses parasitized by thelytokous T. brassicae (6.01) was significantly higher than B strain (2.88). Therefore, this thelytokous line of Trichogramma might be superior to bisexual conspecifics under more natural conditions and hence have a higher potential in pest control.