EFFECTS OF PLANT FLAVONOIDS AND OTHER ALLELOCHEMICALS ON INSECT CYTOCHROME-P-450 DEPENDENT STEROID HYDROXYLASE-ACTIVITY

The plant flavonoids flavone, chrysin, apigenin, kaempferol, morin, qu ercetin, myricetin and phloretin were found to inhibit in a dose-depen dent manner the cytochrome P-450 dependent ecdysone 20-monooxygenase a ctivity associated with adult female Aedes aegypti, wandering stage la rvae of Drosophila melanogaster, and fat body and midgut from prewande ring and wandering stage last instar larvae of Manduca sexta. The conc entrations of these flavonoids required to elicit a 50% inhibition of the steroid hydroxylase activity in all the insects. ranged from ca 1 x 10(-5) to 1 x 10(-3) M. In addition, lower concentrations (1 x 10(-6 ) to 1 x 10(-5) M) of the flavonols kaempferol, morin, quercetin and m yricetin significantly stimulated (50-100% above control) M. sexta fat body ecdysone 20-monooxygenase activity. Other plant allelochemicals examined and found to significantly inhibit insect ecdysone 20-monooxy genase activity include corynanthine, quinidine, and quinine; whereas, indican and mimosine were found to significantly stimulate M. sexta f at body steroid hydroxylase activity. Several allelochemicals were wit hout effect at all concentrations tested. Although none of the compoun ds tested in this study elicited effects at very low concentrations (1 x 10(-9) to 1 x 10(-8) M), the in vitro monooxygenase radioassay does hold considerable promise as a screening tool for the detection and i dentification of plant allelochemicals which may function as biopestic ides affecting insect ecdysteroidogenesis.