Influence of three diets on susceptibility of selected insecticides and activities of detoxification esterases of Helicoverpa assulta (Lepidoptera: Noctuidae)

The oriental tobacco worm, Helicoverpa assulta Guenee, is one of the most destructive pests of tobacco and peppers in China. We determined the susceptibility of H. assulta reared on an artificial diet, chili pepper and tobacco to four insecticides (fenvalerate, phoxim, methomyl, indoxacarb) under laboratory conditions associated with the activities of acetylcholinesterase (AChE), carboxylesterase (CarE) and glutathione S-transferase (CST) in its larvae. H. assulta larvae that were fed with chili pepper were more susceptible to fenvalerate, indoxacarb, and phoxim than those that were fed with tobacco and the artificial diet, but not to methomyl. The larvae that were fed with chili pepper were 3.65-, 2.49-, 1.92- and 2.44-fold more susceptible to fenvalerate, phoxim, methomyl, and indoxacarb than those fed with tobacco, respectively. The AChE activities of H. assulta larvae that were fed with chili pepper and tobacco were 2.12 and 1.07 mu mol mg(-1) 15 min(-1), respectively, almost 2-fold difference. The CarE activity of H. assulta larvae that were fed with chili pepper, tobacco and the artificial diet was 4.12, 7.40 and 7.12 mu mol mg(-1) 30 min(-1), respectively. Similarly, the CST activities of H. assulta larvae that were fed with chili pepper, tobacco and the artificial diet was 52.02, 79.37 and 80.02 mu mol mg(-1) min(-1), respectively. H. assulta larvae that were fed with chili pepper were more resistance to the tested insecticides. The low activities of AChE and the high activities of CarE and CST lead to H. assulta become more susceptible to the tested insecticides. (c) 2009 Elsevier Inc. All rights reserved.