Studies On Fitness, Drought Resistance And Cold Tolerance In Isogenic Cry1 Ac Resistant Strain Of Helicoverpa Armigera (Hübner)

Since transgenic Bt cotton has been commercial planted in 1996, cotton bollworm (CBW) (Helicoverpa armigera (Hübner)) and other target insects have been controlled by it. However, the tolerance and resistance of CBW to Bt cotton will be influenced under this high level selection pressure of Bt toxin. The resistance monitoring in long-term showed that the tolerance of CBW to Bt cotton has constantly increased in the filed. High dose and refuge strategy was an effective method to delay the resistance development. The effect of different hosts on develpoment in resistant and susceptible CBW and the oviposition, distribution and survival of CBW on different hosts, were the important theoretical basis for refuge strategy. CBW overwinter by the diapause pupal at most cotton plant area in China, comparing overwinter differences between resiatant and susceptible strains had the important meaning for researching resistance current in the field and making logical resistance management strategy. In this dissertation, we used the isogenic Bt-Cry1Ac CBW strain as material to study the resistance, it is the first time in China. The differences between resistant and susceptible CBW strains were compared in development changes on different hosts, the oviposition habit among hosts and the drought resistance and cold tolerance. The results were as follows:1. The resistant strain had obvious fitness cost. Compared with susceptible strain, the survival rates of resistant strain decreased and development times delayed feeding on conventional cotton. The survival rates of resistant strain were also lower than susceptible strains feeding on corn, soybean and peanut separately. The larval mortalities of resistant strain feeding on two kinds of transgenic cotton were significant lower than susceptible strain, in despite of the larvae could not pupate.2. We found there were significantly correlation between Bt protein expressed in 33B cotton at different growth periods and mortality rates of resistant and susceptible strains at different treated days. The survival rates of resistant strain were obviously higher than susceptible strain feeding on 33B cotton at each growth periods, they could tolerate the higher selection pressure.3. The peak of oviposition occurred for resistant, susceptible and resistant×susceptible treatments after moths were transferred into cages 3-4 days. There were no differences among three treatments when they oviposited on cotton. The numbers of laid eggs between resistant and susceptible strains were no differences when they oviposited on corn. We found susceptible CBW oviposited more percentage eggs on corn, but three treatments were less rate on soybean and peanut. More hatched larvae survived on corn and cotton. This means corn and cotton are perfect host for oviposition for CBW.4. The emergence rates had no differences between resistant and susceptible strain with different soil moisture content, but the emergence times prolonged in resistant strain for 1-2 days than susceptible strain. The supercooling points (SCP), freezing points (FP), moisture content, fat content, content of glycogen were no differences between resistant and susceptible strains when they fed normal artifical diet, so the cold hardiness was no difference between resistance and susceptible strain .