Resistance Selection And Sublethal Effects Of Emamectin Benzoate In Cotton Bollworm, Helicoverpa Armigera (H(?)bner)

Cotton bollworm, Helicoverpa armigera (Hübner) is a pest belonging to lepidoptera, noctuidae, which is a worldwide important agricultural pest. H. armigera has developed different degree resistance to insecticides of organochlorine, organophosphate, carbamate, and pyrethroids. Emamectin benzoate is a naturally-derived macrolide, antibiotics insecticide and acaricide, which has a high toxicity and efficacy to H. armigera. The use of insecticides may result in multiple sublethal effects, resistance risk, along with direct mortality.1. Realized heritability of resistance and cross-resistance to emamectin benzoate in Helicoverpa armigera (Hübner)In order to evaluate the resistance risk of H. armigera to emamectin benzoate, the resistance selection and realized heritability of H. armigera were estimated in the laboratory. The resistance-selected population(RP25) developed 2.974-fold resistance to the insecticide comparing with the homologous control population (CP), after 25 generations of resistance selection with emamectin benzoate. Realized heritability (h2) of resistance in selection stages was evaluated based on the Tabashnik's methods. The results showed that h2 for the entire selection experiment was 0.05218. To predict the development of resistance, it required 18.67 and 26.71 generations of H. armigera to obtain 5-fold and 10-fold increase of emamectin benzoate in LC50 under selection pressure at 90% mortality for each generation of selection. The bioassay of cross-resistance revealed that the LC50 values of avermectin was 3.962-fold higher in resistance-selected population than that in the homologous control population, suggesting that emamectin benzoate-selected pest had cross-resistance to avermectin.2. Effects of sublethal dose of emamectin benzoate on activities of detoxifying enzymes in Helicoverpa armigera (Hübner) of different sensitivityAfter 20 times of resistance selection with emamectin benzoate, the resistance-selected population (RP20) developed 2.32-fold lower sensitivity to the insecticide comparing with the homologous control population (CP). The 3rd larvae of the two populations were treated with the LC25 dose of emamectin benzoate for 48 h, and then activities of carboxylesterase (CarE) and glutathione-s-transferase (GST) at 3rd, 4th, 5th and 6th instars were determined for analyzing. The resultts showed as follows: (1) With age increasing, activities of CarE increased significantly, and GST tend to stable after lowing in both CP and RP20. (2) Compared with the CP under control treatment(CK), activities of CarE of RP20 increased at 3rd to 6th instar and significantly changed at 4th to 6th instar, however, activities of GST of RP20 was not markedly changed but significantly increased at 3rd and 4th instars. (3) Compared with CK treatment, activities of CarE in both populations increased by LC25 treatment. And activities of GST of CP significantly increased at 4th and 6th instars but was not markedly changed at 3rd and 5th instars, however, activities of GST of RP20 decreased significantly at 3rd instar but was not markedly changed at 4th to 6th instars.The preliminary investigations suggested that the sensitivity of emamectin benzoate to H. armigera decreased may related with activities of CarE, and activities of CarE was induced by sublethal dose of emamectin benzoate. 3. Sublethal effects of emamectin benzoate on the biological performance of Helicoverpa armigera (Hübner) and the life table were builtIn order to study sublethal effects of emamectin benzoate on H. armigera, the 3rd larvae of the homologous control population (CP) were treated with the LC25 of emamectin benzoate for 10 generations, then the sublethal population (Sub10) were obtained. The biological performance, life table parameters of two populations (CP and Sub10), and everyone of populations under different treatment (CK and LC25) were compared and analysed. The results showed that the growth was delayed, pupation rate, emergence rate, fecundity and egg hatching rate were reduced, and adult wing-crippled rate was increased in both populations which were exposured to LC25. these results were also found in Sub10 compared with CP. H. armigera exposed with sublethal dose of emamectin benzoate during the larvae stage had negative effects on population increase [i.e. lower net reproductive rate (R0), intrinsic rate of increase (rm) and finite rate of increase (λ) values, and longer mean generation time (T) and population doubling time (Dt) ]. Such effects were significant in CP, and were not significant in Sub10 but rm and T. There effects about life table parameters were not significant difference between two populations under CK. These results suggested that sublethal dose of emamectin benzoate disadvantages the development and reproduction of H. armigera, and weaken with the generation exposed to pesticide expansion.