Effects Of The Transgenic Bt (Bacillus Thuringiensis) Cotton On Insect Community

The resistance of cotton bollworm to pesticide brings great economic loss to cotton planting. The exploitage of transgenic Bt cotton makes it possible to cotton bollworm.In the laboratory when the first-instar larvae ,third-instar larvae, and fifth-instar larvae of cotton bollworm fet with all kinds of tissues of transgenic Bt cotton, the result showed that transgenic Bt cotton can easily cause death to low-instar larvae and this effect deteriorates on high-instar larvae. Transgenic Bt cotton mainly affect high-instar larvae by retarding the growth and intering the proceeding of ecdysis, pupation, and eclosion. The growth retardation leads to the postponement of growth period duration (The showed that growth period duration prolonged 17 days). Feeding the larvae with the tissue of the transgenic Bt cotton and the moths with the flower of transgenic Bt cotton, the number of eggs and hatching rate decreased obverviously. Transgenic Bt cotton produce an effect on cotton bollworm larvae' s action. The larvae feeding with trangenic Bt cotton spent only 8% of time on feeding and the time on spin-down, locomotion, resting increased highly, while the larvae feeding with traditional cotton spent 50% of time on feeding.The structures of arthropod communities were studied in three areas i.e. pesticide control (PCA), natural enemies control (NECK) in transgenic Bt cotton and integrated pest management (CKA). The results showed that the structures of arthropod communities in transgienic Bt cotton fields weredifferent from that in traditional cotton field. The numbers of order, family, species, and the individual number in transgenic Bt cotton field were more than that in traditional cotton field. The diversity index showed that NECA> PCA> CKA, and so did the evenness index. The dominant concentration index showed that CKA>PCA>NECK. So the stability of the arthropod community in NECA is best and that in CKA is worst in the three areas.Transgenic Bt cotton gravely affect the population dynamic of pests and their natural enemies. The numbers of the Cotton Bollworm in two pieces of transgenic Bt cotton fields were obviously lower than that in traditional cotton field. The Cotton Bollworm had not been the domiant pest in transgenic Bt cotton field, but the number of Aphids, Ded spider mite, Whitefly and so on, increased obviously. The numbers of species and population of the natural enemy sub-community in transgenic Bt cotton field were more than that in traditional cotton field.The analysis of seasonal change of arthropod community in transgenic Bt cotton field could be classified as three stages, the first stage was from May to the end of June, the second stage was from July to the end of August, the third stage was after September.