The bark of Malagasy medicinal plants (Cinnamosma species; family Canellaceae) is enriched in bioactive drimane sesquiterpenes. We previously demonstrated that the most abundant drimane sesquiterpene is a dialdehyde, cinnamodial (CDIAL), that shows promising insecticidal, antifeedant, and repellent activities against Aedes aegypti mosquitoes. To generate insights into the mode of insecticidal action for CDIAL, we examined its effects in vitro on the contractile activity of the ventral diverticulum (crop) of adult female Ae. aegypti. The crop is a food storage organ surrounded by a network of visceral muscle that spontaneously contracts in vitro. Notably, CDIAL completely inhibited spontaneous contractions of the crop and those stimulated by the agonist 5-hydroxytryptamine. Morphometric analyses of crops treated with CDIAL suggested that the compound induced a tetanic paralysis that was dependent on extracellular Ca2+ and inhibited by non-specific blockers of plasma membrane Ca2+ channels. Intriguingly, a Ca2+ ionophore (A23187) elicited similar effects as CDIAL on crop contraction frequency and morphometrics. In conclusion, our results suggest that CDIAL induces a tetanic paralysis of the crop by elevating intracellular Ca2+ through the activation of plasma membrane Ca2+ channels, which may explain the insecticidal effects of CDIAL against mosquitoes.
