Olfactory co-receptor identification and expression pattern analysis in polyembryonic endoparasitoid Macrocentrus cingulum

Abstract

The wasp, Macrocentrus cingulum, is a polyembryonic endoparasitoid from the insect order Hymenoptera deployed successfully as biological control agent for the control of corn pest insect species from the Lepidopteran genus Ostrinia. As an insect, olfaction plays a crucial role for foraging, host-seeking, mating, ovipositing and avoiding toxic substances. Consequently, the molecular basis of olfaction in this wasp is of particular interest. In an effort to expand our understanding of chemosensory pathways, transcripts encoding the highly conserved insect odorant co-receptor (Orco) were isolated from this wasp. The McinOrco shares high degree of sequence homology with known Orco proteins in other insects. Real-time PCR experiments indicate that the McinOrco is expressed mainly in adult antennae, with expression levels differing by sex. The expressing cells were visualized by adapting a whole mount fluorescence in situ hybridization method. Orco-expressing sensory neurons were shown to be abundant in all 39 segments of male antenna. The highest densities of Orco-expressing cells were identified in segment 20, whereas segment 7 comprised in low level. In case of female antenna, levels of Orco-expressing cells were lower than male antenna. Almost expressed cells were distributed over 40 flagellomeres, with decreasing numbers towards the proximal end. These demonstrate the sexual dimorphism concerning the expression cells of Orco. We are the first to report, Orco in polyembryonic endoparasitoid M. cingulum, which play an important role in detection of olfactory cues in this wasp.