Nonanal modulates oviposition preference in female Helicoverpa assulta (Lepidoptera: Noctuidae) via the activation of peripheral neurons

BACKGROUND The insect olfactory system can recognize odorants for feeding, courtship, oviposition and avoiding natural enemies. Odorant cues from host plants play important roles in insect behaviours. Tobacco (Nicotiana tabacum) is the main cultivated host of the oriental tobacco budworm Helicoverpa assult. Volatiles of tobacco plants attract and stimulate oviposition in female moths. However, it is still not known how female H. assulta recognize tobacco volatiles and which odorant compounds are used as oviposition cues. RESULTS We detected 14 volatile compounds emitted from a tobacco plant during vegetative growth, using gas chromatography-mass spectrometry. Electroantennogram tests indicated that eight of the 14 compounds induced responses in female H. assulta. Among these eight volatiles, nonanal greatly increased oviposition preference. Single-sensillum recording (SSR) results showed that many neurons housed in three types of short basiconic sensilla and four types of long basiconic sensilla responded to nonanal and heptanal as its structural analogue. The responses to nonanal were significantly stronger than those to the other compounds. Nonanal was the main ligand of OR67, an odorant receptor from H. assulta. This was demonstrated using an in vitro Xenopus oocytes expression system that supported the SSR results. CONCLUSION Nonanal is a key signal volatile of tobacco plants that attracts female H. assulta moths to oviposit.