Chestnut tannin induces gut degeneration in Aedes albopictus mosquito larvae

In integrated vector management programs, botanicals with insecticidal activity are promising tools, as they are generally not associated with resistance and are characterized by low environmental persistence and reduced non-target toxicity. In the present work, two condensed tannins from black wattle and quebracho (BW and QB, respectively) and two types of hydrolysable tannins from chestnut (CT1 and CT2) were tested for larvicidal activity on Aedes albopictus (Diptera Culicidae). CT2 was the most effective on third-instar larvae after 24 h of exposure (LC₅₀ = 0.56 g L^-1). Gut ultrastructural characterization observed through TEM indicated that, after treatment, the midgut epithelium degenerates, with evident modifications of microvilli and the peritrophic membrane. To unveil the reasons behind the higher bioactivity of CT2, the tannins were examined and compared through elemental analysis and spectroscopic, chromatographic, and mass spectrometric techniques. By these means, differences in the content of minor components between CT1 and CT2 were evidenced, even though their identity could not be ascertained. Lastly, we assessed the oviposition deterrence exerted by CT2 on Ae. albopictus females in the field as a complementary activity. In conclusion, CT2 appears to be a promising tool for the control of Ae. albopictus larvae and gravid females, even if its full chemical characterization still needs to be elucidated.