ABSTRACT
Nociception is the sensory perception of noxious chemical stimuli. Repellent behavior to avoid noxious stimuli is indispensable for survival, and this mechanism has been evolutionarily conserved across a wide range of species, from mammals to insects. The transient receptor potential ankyrin 1 (TRPA1) channel is one of the most conserved noxious chemical sensors. Here, we describe the heterologous stable expression of Tribolium castaneum TRPA1 (TcTRPA1) in human embryonic kidney (HEK293) cells. The intracellular Ca2+ influx was measured when two compounds, citronellal and l-menthol, derived from plant essential oils, were applied in vitro using a fluorescence assay. The analysis revealed that citronellal evoked Ca2+ influx dose-dependently for TcTRPA1, whereas l-menthol did not. In combination with our present and previous results of the avoidance-behavioral assay at the organism level, we suggest that TcTRPA1 discriminates between these two toxic compounds, and diversification in the chemical nociception selectivity has occurred in TRPA1 channel among insect taxa.
ABSTRACT
BACKGROUND: Among insects, beetles are one of the most destructive pests of agricultural and stored products. Researchers have been investigating alternatives to pesticides for more sustainable pest management. Here, we focused on insect transient receptor potential (TRP) channel-targeted repellency. Among transient receptor potential melastatin (TRPM) channels, mammalian TRPM8 is activated by menthol and its derivatives, but few previous studies have reported on whether the insect TRPM channel is activated by chemical compounds. Here, we investigated whether the TRPM channel (TcTRPM) of the red flour beetle Tribolium castaneum (Herbst), a major stored-products pest, mediated the repellent behavior of l-menthol and its derivatives. RESULTS: We initially investigated the repellent activity of l-menthol and menthoxypropanediol (MPD) against T. castaneum. The laboratory bioassay revealed that the repellent activities of l-menthol and MPD were dose dependent. RNA interference was used for transcriptional knockdown of TcTRPM and revealed that a reduced transcript level resulted in a significant decrease in l-menthol and MPD repellent activities. However, no significant decrease was observed for N,N-diethyl-3-methylbenzamide (DEET) repellency. The most abundant TcTRPM transcripts were observed in the antennae. However, antennae-plucked beetles maintained their repellent behavior with l-menthol. CONCLUSION: The repellent activities of l-menthol and MPD for T. castaneum are mediated by TcTRPM, and it was suggested that the olfactory response is not adequate for avoidance, but that contact repellency might be a more important repellant method. © 2020 Society of Chemical Industry.
