Biphasic Dose–Response of Components From Coptis chinensis on Feeding and Detoxification Enzymes of Spodoptera litura Larvae

Due to long-term coevolution, secondary metabolites present in plants apparently function as chemical defense against insect feeding, while various detoxification enzymes in insects are adaptively induced as a prosurvival mechanism. Coptis chinensis, a medicinal plant used in traditional Chinese medicine for a thousand years, was found to be less prey to insects in our earlier field observations. Herein, 4 crude extracts obtained from sequential partition of aqueous extract of Rhizoma coptidis with petroleum ether, ethyl acetate, and n-butanol exhibited antifeedant activity against Spodoptera litura (Fabricius) larvae at high doses and inducing activity at low doses. Furthermore, a similar biphasic dose–response of the antifeedant activity against S litura larvae was also observed for jateorhizine, palmatine, and obakunone in Coptis chinensis. Notably, the enzyme activities of glutathione-S-transferase and carboxyl esterase in S litura larvae affected by the different components (jateorhizine, palmatine, obakunone, berberine, and coptisine) of C chinensis also showed a biphasic dose–response with an increasing trend at low doses and a decreasing trend at high doses. Together, our study suggests that the components of C chinensis may play a chemical defensive role against S litura larvae in a hormetic manner.