ACTIONS OF AZADIRACHTIN, A PLANT ALLELOCHEMICAL, AGAINST INSECTS

Investigations of the antifeedant mode of action of azadirachtin and f our synthetic analogues, 22,23-dihydroazadirachtin, 3-tigloylazadirach tol, 11-methoxydihydroazadirachtin and 22,23-bromoethoxydihydroazadira chtin have revealed that both polyphagous and oligophagous insects are behaviourally responsive to azadirachtin, with the most responsive sp ecies being able to differentiate extremely small changes in the paren t molecule. In Lepidoptera the antifeedant response is correlated also with increased neural activity of the chemoreceptors. When locusts ar e treated on crop plants, the antifeedant and physiological actions of azadirachtin and analogues work in concert and result in feeding dete rrence, growth and moulting aberrations and mortality with the same or der of potency as for antifeedancy. Specific binding studies using [H- 3]dihydroazadirachtin carried out on locust testes and Spodoptera Sf9 cells have shown that the competitive binding of the different analogu es of azadirachtin to these binding sites occurs in a similar order of potency to that found with antifeedant and IGR bioassays. This sugges ts a causal link between specific binding to membrane proteins and the ability of the molecule to exert biological effect. (C) 1998 Society of Chemical Industry.