Risk Assessment Of Transgenic Bt Cotton On Cotton Aphid, Aphis Gossypii Glover (Homoptera: Aphididae)

GK12 was one of the transgenic Bt cotton varieties developed by Chinese scientists and commercialized on a large scale. In this study, GK12 was used to evaluate the effects of transgenic Bt cotton on the non-target pest cotton aphid. Bt protein determination in cotton plant and cotton aphid, detection of detoxification enzyme activities, digestive enzyme activities and insecticide susceptibility of cotton aphid, life-table parameters measurement such as survival, development and reproduction were involved in this study. Especially, the long-term impacts of transgenic Bt cotton on cotton aphid were emphasized. The main results were as follows:1. The impacts of transgenic cotton on the basic biology of cotton aphids were measured in laboratory with the method of life-table. The results showed that both transgenic Bt cotton GK12 and transgenic Bt+CpTI cotton SGK321 had no significant impacts on the mortality, development and life-table parameters of cotton aphids. Comparing to those of cotton aphids fed on the corresponding parental non-transgenic cotton variety, development and mortality of the four instar larvae, mass and longevity of adult, reproduction period and number of offspring, life-table parameters of cotton aphid fed on SGK321 for one generation did not differ significantly. That's the same for cotton aphids fed on GK12 for both one and 37 generations. These indicated that GK12 and SGK321 had no direct acute toxic effects and no adverse impacts on the development and reproduction of cotton aphids. These indices did not differ significantly between cotton aphids fed on GK12 for one generation and for 37 generations, thus indicated that transgenic Bt cotton had no adverse effects on the biological parameters of cotton aphids for the long run. Development of cotton aphids was also not affected significantly when fed on artificial diets containing Cry1 Ac protoxin at different concentrations.2. Bt protein concentration detection by ELISA showed that Bt concentrations were higher in leaves and pollen both in transgenic Bt cotton cv. GK12 and in transgenic Bt+CpTI cotton cv. SGK321. And the Bt concentrations in SGK321 were higher than those in GK12. Further study showed that Bt protein concentration in GK12 leaves varied with cotton development, Bt concentrations from high to low were: four-cotyledon stage leaves two true-leaf stage leaves >boll stage leaves. Trace amount of Bt protein could be detected partly in phloem sap and nectar samples. Bt protein could also be detected partly in adult aphids and their honeydew, but could only be detected in the samples of over 300 adults. Bt protein concentration in honeydew was higher than that in adults and increased with the feeding generations.3. The activities of detoxification enzyme and AchE in cotton aphids fed on Bt cotton GK12 for different generations were determined with microtiter plate reader. The results showed that there was no significant difference in activities of esterase, carboxylesterase and AchE among cotton aphids fed on GK12 for one and for 21 generations and those fed on Simian 3. There was no significant difference between cotton aphids fed on GK12 for one generation and 21 generations. Besides, the enzyme activityfrequency distributions of the three enzymes of cotton aphids fed on Bt cotton were similar to those of cotton aphids fed on non-Bt cotton, indicating that transgenic Bt cotton had no adverse effects on the detoxification enzymes of cotton aphids both in the short and and in the long terms. When continuously fed on GK12 for different generations, Vmax and Km of esterase and AchE in cotton aphids did not differ significantly from those of cotton aphids fed on Simian 3, indicating that transgenic Bt cotton had no adverse effects on the structure and the affinity of the two enzymes to ubstrate.4. The activities of digestive enzymes of cotton aphids fed on GK12 for different generations were detected with microtiter plate reader. The results showed that there was no significant difference of proteinase activities, amylase activities, trehalase activities and sucrase activities among cotton aphids fed on GK12 for one generation, two generations, three generations and over sixty generations, and cotton aphids fed on Simian 3. It indicated that transgenic Bt cotton had no significant adverse effects on digestive enzymes activities of cotton aphids both in the short and and in the long terms.5 Insecticide susceptibility of cotton aphids fed on transgenic Bt cotton were determined in laboratory, and four kinds of insecticides including of imidacloprid, phoxim, deltamethrin and methomyl were involved in the study. The results indicated that transgenic Bt cotton did not affect the insecticide susceptibility of cotton aphids. LC50 and LC90 of cotton aphids fed on GK12 for one to three generations and over sixty generations did not differ significantly to those of cotton aphids fed on Simian 3. Slope b of toxicity regression curve did not differ either. It indicated that the susceptibility of cotton aphids to imidacloprid, phoxim, deltamethrin and methomyl was not affected by transgenic Bt cotton even though they fed on Bt cotton for over sixty generations. Among the four insecticides tested, their resistances to cotton aphid ranked from strong to weak were: imidacloprid > methomyl > phoxim > deltamethrin.