Damages evaluation of Bt. transgenic cotton to cotton bollworm, Helicoverpa armigera (Hubner)

Studies were carried out at Nakhon Sawan Field Crops Research Center, Si Samrong Field Crops Experiment Station, Sukhothai province and Loei Field Crops Experiment Station during June 1997-January 1998. The Bt. transgenic cotton varieties, NuCOTN 33*[B) and NuCOTN 35*[B), were compared with recommended cotton varieties, Srisamrong 60, DP 5415 (non Bt. transgenic) and Sudan. Strip plot design with 4 replications was used in the experiment. The treatments consisted of 2 main plots, treated and untreated of insecticides and tested cotton varieties as subplots. The results obtained indicated that the Bt. transgenic cotton was resistant to the cotton bollworm in every location where the experiment was conducted. The smallest number of cotton bollworm was found on the Bt. transgenic cotton as compared to those found on Srisamrong 60 and other cotton varieties tested. Under the severe outbreak of cotton bollworm in Nakhon Sawan the yield of the Bt. transgenic cotton was higher than those of Srisamrong 60 and other cotton varieties. The average yields obtained from the Bt. transgenic cotton were 464 and 433 kgs/rai while those obtained from Srisamrong 60 were 151 and 16 kgs/rai in the sprayed and nonchemical -sprayed conditions respectively. Under the low incidence of cotton bollworm the yields of the Bt. transgenic cotton and of Srisamrong 60 were almost the same. The average yields obtained from the Bt. transgenic cotton were 264 and 213 kgs/rai while those obtained from Srisamrong 60 were 195 and 187 kgs/rai under the chemical and nonchemical sprayed conditions respectively. At Loei Field Crops Experiment Station where there was an outbreak of cotton leaf curl disease, the average yield of the Bt. transgenic cotton was lower than that of Srisamrong 60. This is due to the susceptibility of the Bt. transgenic cotton and the resistance of Srisamrong 60 to the disease. The average yields obtained from the Bt. transgenic cotton were 266 and 264 kgs/rai while those obtained from Srisamrong 60 were 381 and 314 kgs/rai under the chemical and nonchemical sprayed conditions respectively.