Article ID: G10-52
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. Khayasin (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 2′S-methylbutanoylproceranolide (2) displayed marked insecticidal activity against fifth-instar larvae of the same pest at the same concentration. LC50 (concentration of 50% lethal rate) 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 1–2 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 1–2 only exhibited moderate antifeedant activities against third-instar larvae of Prodenia litura (Fabricius). These results suggested that compounds 1–2 had selectively insecticidal activities against the larvae of B. longissima. They are promising candidate insecticides for the control of B. longissima.
