The larvae of Phyllotreta striolata share the same olfactory cues for locating Brassicaceae plant with conspecific adults

The sophisticated olfactory system of insects plays crucial roles in host plant location. In comparison with comprehensive studies on the molecular mechanisms of olfactory cues detection in lepidopteran moths, little is known about how coleopteran beetles detect host plant cues. Phyllotreta striolata is a devastating coleopteran pest of Brassicaceae crops, and its larvae feed on roots underground, while its adults destroy leaves aboveground. In this study, we focus on the molecular basis of olfactory cues detection in P. striolata and attempt to determine whether P. striolata larvae share the same specific olfactory cues for host plant location with conspecific adults and whether the detection mechanism is conserved. A two-choice behavioral bioassay was conducted to examine the behavioral responses of P. striolata to different types of isothiocyanates (ITCs), which are the characteristic volatiles of Brassicaceae crops. The results showed that both P. striolata adults and larvae were attracted by allyl ITC, although adults showed a broader behavioral response range. The transcriptome sequencing of P. striolata adults and larvae was performed, and 157 chemosensory genes were identified, among which 6 OBPs, 2 CSPs, 1 OR, 1 IR and 1 GR were found to be preferentially expressed in both P. striolata adults and larvae. Functional studies of PstrOBP9, PstrOBP13 and PstrOBP17, three of the six OBPs that were highly expressed in both adults and larvae, revealed that PstrOBP9 strongly bound allyl ITC and eight other ITCs. Taken together, these findings demonstrated that P. striolata larvae and adults could employ the same olfactory proteins to detect specific plant volatiles for host location, which provides a new perspective on the development of environmentally friendly pest management targeting both P. striolata adults and larvae.