Exposure of fouth instars of Spilarctia obliqua Walker (Lepidoptera: Arctiidae) to excelsin over a 24 h period resulted in reduced feeding and growth rates. To distinguish between antifeedant and toxic effects, growth efficiency, calculated as the slope of the regression of the relative growth rate on relative consumption rate, was compared with results from antifeedant simulation and contact toxicity bioassays. From the results, it is concluded that excelsin exerts its toxic effects at the physiological level.

Crude fractions of aerial parts of Andrographis paniculata (Burm.f.) (Acanthaceae) were evaluated for antifeedant, growth-inhibitory and oviposition-deterrent activity against larval and adult stages of the Bihar hairy caterpillar, Spilarctia obliqua (Arctiidae). The methanol fraction had the highest growth-inhibitory activity. Further fractionation resulted in nine sub-fractions of which the most active, identified as the diterpene andrographolide, displayed significant growth-inhibitory and antifeedant properties with GI50 and FD50 values of 100.4 and 159.7 μg/g diet respectively. The ethyl acetate fraction possessed the highest oviposition-deterrent activity.