Mutagenesis of Odorant Receptor Coreceptor Orco Reveals the Odorant-Detected Behavior of the Predator Eupeodes corollae

The successful mating of the hoverfly and the search for prey aphids are of great significance for biological control and are usually mediated by chemical cues. The odorant receptor co-receptor (Orco) genes play a crucial role in the process of insect odor perception. However, the function of Orco in the mating and prey-seeking behaviors of the hoverfly remains relatively unexplored. In this study, we characterized the Orco gene from the hoverfly, Eupeodes corollae, a natural enemy insect. We used the CRISPR/Cas9 technique to knock out the Orco gene of E. corollae, and the EcorOrco(-/-) homozygous mutant was verified by the genotype analysis. Fluorescence in situ hybridization showed that the antennal ORN of EcorOrco(-/-) mutant lack Orco staining. Electroantennogram (EAG) results showed that the adult mutant almost lost the electrophysiological response to 15 odorants from three types. The two-way choice assay and the glass Y-tube olfactometer indicated that both the larvae and adults of hoverflies lost their behavioral preference to the aphid alarm pheromone (E)-beta-farnesene (EBF). In addition, the mating assay results showed a significant decrease in the mating rate of males following the knock out of the EcorOrco gene. Although the mating of females was not affected, the amount of eggs being laid and the hatching rate of the eggs were significantly reduced. These results indicated that the EcorOrco gene was not only involved in the detection of semiochemicals in hoverflies but also plays a pivotal role in the development of eggs. In conclusion, our results expand the comprehension of the chemoreceptive mechanisms in the hoverflies and offers valuable insights for the advancement of more sophisticated pest management strategies.