Behavioural and neurophysiological responses of Spodoptera littoralis to azadirachtin and a range of synthetic analogues

The antifeedant activity of azadirachtin and 56 azadirachtin analogues, including 22, 23‐dihydroazadirachtin, against larvae of Spodoptera littoralis was investigated using behavioural and electrophysiological bioassays. None of the analogues was as active as azadirachtin, although many showed significant antifeedant activity at high concentrations. The majority of the analogues stimulated a dose‐dependent response from a neurone in the medial styloconic maxillary sensilla which correlated with the behavioural activity. Methylation of the hydroxy substitutions on the azadirachtin molecule usually resulted in a decrease in antifeedant activity, as did the addition of bulky groups to the dihydrofuran ring.