Abstract: The effects of four plant allelochemicals，gossypol, nicotine, tomatine and capsicine, on nutritional utilization and detoxication enzymes activities in midgut were investigated with the 5th instar larvae of cotton bollworm, Helicoverpa armigera, and oriental tobacco budworm, H. assulta. The results showed that H. armigera exhibited wide adaptability to all the four allelochemicals, whereas H. assulta could only fit well to nicotine and capsicin, which were the allelochemicals from its host plants. Midgut CarE activity was unaffected by the allelochemicals in H. armigera and H. assulta. GST activity in the midgut of H. assulta could be strongly induced by nicotine and capsicine, but significantly inhibited by tomatine; none of the four allelochemicals could affect midgut GST activity in H. armigera.

Key words: plant allelochemicals, Helicoverpa assulta, H. armigera, nutritional indices, detoxication enzymes