Olfactory response of Trichogramma pretiosum (Hymenoptera: Trichogrammatidae) to volatiles induced by transgenic maize

Abstract

Plants not only respond to herbivorous damage but adjust their defense system after egg deposition by pest insects. Thereby, parasitoids use oviposition-induced plant volatiles to locate their hosts. We investigated the olfactory behavioral responses of Trichogramma pretiosum Riley, 1879 (Hymenoptera: Trichogrammatidae) to volatile blends emitted by maize (Zea mays L.) with singular and stacked events after oviposition by Spodoptera frugiperda Smith, 1797 (Hymenoptera: Trichogrammatidae) moths. Additionally, we examined possible variations in gene expression and on oviposition-induced volatiles. We used a Y-tube olfactometer to test for the wasp responses to volatiles released by maize plants oviposited by S. frugiperda and not-oviposited plants. Using the real-time PCR technique (qRT-PCR), we analyzed the expression of lipoxygenase and three terpene synthases genes, which are enzymes involved in the synthesis of volatile compounds that attract parasitoids of S. frugiperda. Olfactometer tests showed that T. pretiosum is strongly attracted by volatiles from transgenic maize emitted by S. frugiperda oviposition (VTPRO 3, more than 75% individuals were attracted). The relative expression of genes TPS10, LOX e STC was higher in transgenic hybrids than in the conventional (isogenic line) hybrids. The GC-MS analysis revealed that some volatile compounds are released exclusively by transgenic maize. This study provides evidence that transgenic hybrids enhanced chemical cues under oviposition-induction and helped to increase T. pretiosum efficiency in S. frugiperda control. This finding shows that among the evaluated hybrids, genetically modified hybrids can improve the biological control programs, since they potentialize the egg parasitoid foraging, integrating pest management.