Identification of the differences in olfactory system between male and female oriental tobacco budworm Helicoverpa assulta.

The olfactory system of insects facilitates their search for host and mates, hence it plays an essential role for insect survival and reproduction. Insects recognize odor substances through olfactory neurons and olfactory genes. Previous studies showed that there are significant sex-specific differences in how insects identify odorant substances, especially sex pheromones. However, whether the sex-specific recognition of odorant substances is caused by differences in the expression of olfaction-related genes between males and females remains unclear. To clarify this problem, the whole transcriptome sequence of the adult Helicoverpa assulta, an important agricultural pest of tobacco and other Solanaceae plants, was obtained using Pacbio sequencing. RNA-seq analysis showed that there were 27 odorant binding proteins (OBPs), 24 chemosensory proteins, 4 pheromone-binding proteins (PBPs), 68 odorant receptors and 2 sensory neuron membrane proteins (SNMPs) genes, that were expressed in the antennae of male and female H. assulta. Females had significantly higher expression of General odorant-binding protein 1-like, OBP, OBP3, PBP3 and SNMP1 than males, while males had significantly higher expression of GOBP1, OBP7, OBP13, PBP2 and SNMP2. These results improve our understanding of mate search and host differentiation in H. assulta.

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. © 2020 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.