Multimodal targets of (‐)‐α‐thujone mediating avoidance behavior of a stored‐products pest, Tribolium castaneum , in response to irritant stimuli

BACKGROUND: The reciprocal evolutionary processes among phytophagous insects and host plants involve host shift in the herbivorous insects in response to defense chemicals, such as plant-derived terpenoid compounds that comprise a key element for adaptive radiation, leading to chemosensory diversification. To reveal the multimodal chemosensory targets mediating avoidance behavior of insects in response to irritant stimuli, in this study, we explored multimodal target molecules toward (-)-α-thujone, a bicyclic monoterpenoid compound, focusing on the red flour beetle, Tribolium castaneum. RESULTS: The area-preference test revealed significant avoidance behavior in adult T. castaneum toward (-)-α-thujone. We applied systemic RNAi methodology to knock down hypothesized targets; knocking down the resistance to a dieldrin (Rdl) subunit comprising a γ-aminobutyric acid (GABA)-activated receptor significantly suppressed the avoidance behavior toward (-)-α-thujone, rather than l-menthol. Avoidance behaviors were significantly suppressed after knocking down thermo (TcTRPM) and non-thermo (TcTRPL) TRP channels. Subsequently, quantitative reverse transcription (qRT)-PCR-based spatial expression analysis of TcRdl and TcTRPL revealed high TcRdl transcript expression in the head, followed by the antenna, and prominent TcTRPL transcript expression in the head. Furthermore, the reduced avoidance behavior in antenna-dissected and knockdown of the olfactory receptor coreceptor (TcOrco) lines confirmed the involvement of antenna in the underlying mechanism. CONCLUSION: The results reflected potential molecular targets including non-thermo TRP channel involved in (-)-α-thujone-mediated avoidance behavior in T. castaneum and indicated multimodality, as exhibited by N,N-diethyl-3-methylbenzamide (DEET), the gold standard of repellent, providing useful insight for further research on the development of new repellents and excito-repellents.