Studies On The Profenofos Resistance In Cotton Bollworm, Helicoverpa Armigera (Hübner)

The resistance of the third instar of cotton bollworm, Helicoverpa armigera (Hubner) collected from four places of Jiangsu, Henan and Hebei Province in 1999 and 2000, was monitored by means of topical application. Except moderate level resistance (18.6-fold) in the colony from Hebei Province, the cotton bollworm from the other places had low level resistance to profenofos. Cotton bollworm had reached or approached moderate level resistance to the other organophosphorus and carbamate insecticides. Except low level resistance to fenvalerate, the cotton bollworm had reached or approached high level resistance.After continuously laboratory selected with high concentration profenofos for 12 generations, the cotton bollworm from Dongtai county, Jiangsu Province exhibited about 7.1-fold resistance to this insecticide as compared with original colony before selection, LD50 value increased from 0. 0469 u g A. I. / larvae before selection to 0.3348ug A. I. / larvae after selection. And after with low concentration profenofos, LD50 value increased from 0. 0469 u g A. I. / larvae before selection to 0.1826 u g A. I. / larvae after selection and this insect developed resistance with 3.9 fold. This showed that resistance developing speed of population selected with high concentration profenofos was much faster than that selected with low concentration profenofos.The cross-resistance to other conventional insecticides in cotton bollworm population selected with high concentration profenofos was measured. The cross-resistance to cyhalothrin, proxim, monocrotophos and deltamethrin was remarkable (4.1-10.4-fold). The cross-resistance to methamidophos and methomyl was general (2.2-2.6-fold).After selected with Bt biological pesticide and transgenic Bt cotton inlaboratory, cotton bollworm had reached high level resistance. LDso of resistant strain and susceptible strain was measured respectively. Increasing resistance folds were 1.1 and 1.5-fold respectively. This showed that the cross-resistance to profenofos in cotton bollworm strain selected with Bt biological pesticide and transgenic Bt cotton was not remarkable, but the cross-resistance to proxim was remarkable (8 fold). So proxim should not be used once serious resistance to trangenic Bt cotton occurred. But using profenofos is suitable.S, S, S-tributylphosphorotrithionate (DBF), synergised profenofos in the third instar larvae of laboratory selected resistant population of H. armigera, with the synergism ratio 2.3-fold, but profenofos was hardly synergised by piperonyl butoxide (Pbo), with the synergism ratio 0.7-fold. This suggested that profenofos resistant mechanism may be concerned in the metabolic mechanism of esterase, but not MFO.According to the method introduced by Tabashnik, estimate of the heritability (h2) of resistance to profenofos in Helicoverpa armigera (Hli bner) was 0.1376. The resistance developing speed of the cotton bollworm is predicted by the result of h2. If under the same situation of laboratory selection and percentage killed by profenofos was 90%, when h2=0.1376, the generations required for 10-fold increase in profenofos resistance were 9. 5. When h2=0. 1282, the generations were 10. 2. If under the same high intension (percentage surviving selection=27. 5%), the generations for 10-fold increase in profenofos resistance were 13.8. If under the same low intension (percentage surviving selection=46.5%), the generations were 21.0. This furthur showed that resistance developing speed of population selected with high concentration profenofos was much faster than that selected with low concentration profenofos.