Khayasin and 2'S-methylbutanoylproceranolide: Promising candidate insecticides for the control of the coconut leaf beetle, Brontispa longissima

Abstract

Brontispa longissima (Gestro) is a serious pest of coconut palms in tropical areas. In our continuing search for potential pesticides from tropical mangrove plants, khayasin (1) and 2′S-methylbutanoylproceranolide (2), two mexicanolides with a Δ8,14 double bond, were isolated from seeds of an Indian mangrove, Xylocarpus moluccensis. The structures of these compounds were established by comparison with data in the literature. Compound 1 was found to exhibit potent insecticidal activities against second- to fifth-instar larvae of B. longissima at a concentration of 50 μg/ml, and compound 2 displayed marked insecticidal activity against fifth-instar larvae of the same pest at the same concentration. LC50 (concentration of 50% mortality) values for compound 1 against fifth-instar larvae of B. longissima at exposure times of 24 and 48 h are 7.27 and 3.39 μg/ml, respectively, and those for compound 2 are 10.57 and 4.03 μg/mL, respectively. The insecticidal activities of compounds 1 and 2 against fifth-instar larvae of B. longissima are more potent than those of azadirachtin and toosendanin, and are similar to those of rotenone; however, compounds 1 and 2 only exhibited moderate antifeedant activities against third-instar larvae of Prodenia litura (Fabricius). These results suggested that compounds 1 and 2 had selectively insecticidal activities against the larvae of B. longissima. They are promising candidate insecticides for the control of B. longissima.