Response of Trichogramma pretiosum females (Hymenoptera: Trichogrammatidae) to herbivore-induced Bt maize volatiles

Abstract

Parasitoids use herbivore-induced plant volatiles (HIPV´s) to locate their hosts. However, little is known about variations in HIPV´s production in genetically modified maize plants that are herbicide tolerant (singular event), insect resistant (Bt plants, singular event), or both herbicide tolerant and insect resistant, like staked events. We investigated the olfactory responses of the egg parasitoid Trichogramma pretiosum (Hymenoptera: Trichogrammatidae) to HIPV´s produced in maize (Zea mays) herbicide-tolerant and insect-resistant plants or their stacked events in response to damage caused by Spodoptera frugiperda during nighttime and daytime infestations. Real-time reverse-transcription PCR was used to assess whether the presence of one or more Bacillus thuringiensis (Bt) proteins and the time of induction of HIPV’s affected the expression of genes in plants under herbivore attack. The results showed that compounds were released during both nocturnal and diurnal infestations. However, some HIPV´s were released exclusively in infestations that started during the night by non-Bt plants and they were highly attractive to parasitoids. HIPV´s produced by non-Bt plants were more attractive to parasitoids than those released by Bt plants in infestations that started during the night. However, glyphosate-tolerant maize plants were more attractive to parasitoids than isogenic plants. The expression of the analyzed genes TPS10, TPS23, LOX10, and STC1 was higher in infestations that started during the night. In this study, we discuss the possible causes of the unresponsiveness of T. pretiosum females to HIPV´s produced by Bt maize.