Ecological Impacts Of Bt Cotton On Target And Non-target Insects In Xinjiang Cotton-growing Region

Recently, more attentions have been paid on the assessment of the impacts of transgenic Bt (Bacillus thuringiensis Berliner) cotton on target and non-target insects. This work studied the temporal and spatial dynamics of Bt toxin protein expression of transgenic Bt cotton, and evaluated the impacts of Bt cotton on the target and non-target pests and natural enemies in Xinjiang cotton-growing region during 2002-2009. The major results are as follows:The content of Bt toxin protein greatly varied between cotton varieties in southern and northern Xinjiang. More specifically, SGK321 (transgenic CrylAc+CpTI cotton) expressed significantly higher level of Bt toxin protein than GK-19 (transgenic CrylAc cotton) in most of cotton organs during the whole cotton development period. The tender leaves produced significantly more Bt toxin protein than squares in southern Xinjiang, whereas no significant differences were found in northern Xinjiang. The contents of Bt toxin protein in the reproductive organs were usually higher than in the vegetative ones in flowering, flowering-boiling and boiling periods, and those in majority of organs (including tender leaf, square, petal, stigma, and flower bract) gradually decreases with cotton plant development. Additionally, the insecticidal protein expressions significantly changed among different years.The development duration of cotton bollworm Helicoverpa armigera larvae feeding on Bt cotton was markedly prolonged at each stage. The weights of 3rd instar larva and pupa were significantly lighter on Bt cotton than on non-Bt cottons, and the survival percentage of larvae is lower on Bt cotton. The field experiments showed that the larval densities varied significantly between Bt and non-Bt cotton irrespective of cotton planting densities, while the egg densities did not.The weight of cotton aphid. Aphis gossypii, and the population densities of A. gossypii, Thrips tabaci, and spider mite are similar in Bt and non-Bt cotton fields.No significant differences were found in population densities of spiders. Hippodamia variegata or predatory bugs in Bt and non-Bt cotton fields. The developmental periods of each instar larva, pre-pupa and pupa of H. variegata feeding cotton aphids on transgenic Bt and non-Bt cotton also were not significantly different among various regions. Additionally, transgenic Bt cotton has no obvious impact on the midgut cylindric epithelial cells of adults and larva of H. variegata.The parameters, such as the total number of individuals and the arthropod species in the insect pest subcommunity, neutral subcommunity, and natural enemy subcommunity, the diversity indices, evenness indices and dominant concentrative indices of the arthropod community, the diversity indices and evenness indices of the insect pest subcommunity and natural enemy subcommunity greatly varied between seasons for each cotton variety, but did not significantly differ in Bt and non-Bt cotton fields.This study clarified the temporal and spatial dynamics of Bt toxin expression in transgenic Bt cotton, and confirmed the impacts on target and non-target pests and natural enemies in arid and semiarid ecological regions in Xinjiang. These results will be available for assessing ecological biosafety of Bt cotton in these regions, and developing a sustainable pest management strategy in Xinjiang.