Studying On The Interaction Between Spodoptera Litura And Transgenic Cotton(Cry1Ac)

Common cutworm, Spodoptera litura, is a polyphagous and occasional pest, which can damage vegetable, soybean, cotton and other important economic crops. Common cutworm most occurs in vegetable fields in the Yangtze River valley this century ago. Since trangenic Cry1Ab/Ac cotton, expressing Cry1A insecticidal protein and aimed at Helicoverpa armigera and Pectinophora gossypiella, has been commercialized from 2000, common cutworm frequently began to attack cotton and casue serious yield loss due to its low susceptibility to Cry1A protein.To elucidate the interaction mechanizm between S. litura and trangenic cotton, in this article, we investigated firstly on the effect of CryAb/Ac trangenic cotton on S. litura feeding behavior and fitness. Secondly, we determined the optimum PH vlaues of S. litura midgut proteases and their activities. In the end, the proteolytic fragments of Cry1Ac protein by midgut proteases of S. litura were analyzed through SDS-PAGE. The main results as follows:1. The effect of transgenic cotton on development and cold hardness of S. lituraTo evaluate the effect of transgenic cotton on fitness of S. litura, bioassay with feeding on fresh leaf was conducted. The result displayed that no significant differences were observed on the survival, development, fecundity and super-cool point of S. litura when feeding on GK19, expressing Cry1A insecticidal protein, or feeding on Simian3, a conventional cotton.2. The effect of transgenic Cry1Ab/Ac cotton on S. litura feeding behaviorThe 1st instar larval of S. litura has no prefence when fed on transgenic cotton or conventional cotton exclusively, and no significantly difference was observed on infected area between two varities. However, the 3rd instar showed preference to GK19.3. The optimum PH values of midgut protease of S. litura and their activitiesThe optimum pH value of mid-gut protease in larvae of S. litura was determined in laboratory. The results showed that the optimum pH values of total protease in S. litura midgut were 7.5. The optimum pH values of active alkaline trypsin-like enzyme, weak alkaline trypsin-like enzyme, and chymotrypsin-like enzyme was 9.5,7.5 and 9.5 respectively.4. The metabolism of S. litura to Cry1Ac proteinThe distribution and content of Cryl Ac insecticidal protein in different tissues and feces of S. litura were determined and analyzed by enzyme-linked immunosorbent assay (ELISA), when the 5th instar larvae fed on top leaves of transgenic Bt cotton expressing Cryl Ac protein for 3 days. The result of determine suggested that the Cryl Ac protein was found in S. litura gut, Malpighian tubule, fat body, haemolymph, and other tested parts. All of parts, the Cryl Ac content in feces were the highest with 2989ng/ml, and those in haemolymph were the lowest with 3ng/g.In addition, we also investigated the proteolytic processing to Cry1Acδ-endotoxin in vitro by using gut juice purified from S. litura and Helicoerpa armigera. The result displayed that Cry1Ac was processed to an insoluble product with a molecular mass of～60 kDa in S. litura midgut, whereas it was generated products with molecular masses of～65 and～38 in H. armgiera.