Variations in Composition of Alkanes and Free Fatty Acids in Aulacophora foveicollis Lucas (Coleoptera: Chrysomelidae) on Exposure to Monocrotophos

Abstract

Aulacophora foveicollis Lucas (Coleoptera: Chrysomelidae) is an important herbivore pest of cucurbitaceae, which is currently controlled by insecticides in southeast Asia. The insect cuticle is the first line of defence against insecticides. So, we investigated the variations in the composition of n-alkanes and free fatty acids (FFAs) in cuticular and internal lipids of A. foveicollis males and females exposed to monocrotophos compared to untreated adults. Both sexes of A. foveicollis adults were dipped in petroleum ether for 1 min at room temperature for extraction of surface waxes, and the insects were further kept in dichloromethane for 15 days for extraction of internal lipids. n-Alkanes and FFAs of cuticular and internal lipids were identified and quantified by GC–MS and GC–FID analyses. Higher quantities of cuticular lipids were observed in males and females exposed to monocrotophos than untreated males and females. Twenty n-alkanes were identified between n-C15 and n-C36 in cuticular lipids of untreated A. foveicollis adults; whereas 21 n-alkanes were detected in cuticular lipids of treated adults. Nineteen FFAs were recorded between C10:0 and C22:0 in cuticular lipids of untreated adults; whereas 21 and 19 FFAs were recorded in cuticular lipids of treated males and females, respectively. Hentriacontane and palmitoleic acid were the predominant n-alkane and FFA in the cuticular lipids of treated males and females, respectively. This study revealed that change of alkanes and FFAs in cuticular lipids of A. foveicollis males and females are linked to exposure to monocrtophos, which might result in increasing resistance of A. foveicollis.