The cotton bollworm, Helicoverpa armigera, is one of the most serious insect pests of cotton, corn, peanut, vegetables, and other crops throughout Asia. There are four or five generations of cotton bollworm per year in northern China and overwinters as a diapausing pupa. Previous research indicated that transgenic Bt cotton affect development and reproduction of the cotton bollworm, and that a marked decrease in regional outbreaks of the cotton bollworm in multiple crops was associated with the planting of transgenicBt cotton. However the effects of transgenic Bt cotton on the overwintering generation of the cotton bollworm are unknown.

Researchers at Institute of Zoology, Chinese Academy of Sciences used transgenic Bt cotton as a diet of the cotton bollworm to explore the effects of transgenic Bt cotton on overwintering characteristics and survival of the pest. Results by field and laboratory experiments showed that larvae of the pest fed on Bt cotton had a decreased pupation rate, and fewer entered diapause and emerged as adults compared with larvae fed non-Bt cotton. Furthermore, larvae fed Bt cotton had reduced pupal weight, glycogen content and trehalose levels both in diapausing and in non-diapausing pupae, and only diapausing pupae had an increased supercooling points(SCPs) compared to controls. The SCPs of diapausing pupae reared on Bt cotton were significantly higher than those reared on non-Bt cotton. The trehalose levels of diapausing pupae reared on Bt cotton were significantly lower than those of larvae reared on non-Bt cotton.

Thus, in the study the researchers suggest that a Bt cotton diet weakens the preparedness of cotton bollworm for overwintering and reduces survival of the overwintering generation, which will in turn reduce the density of the first generation in the following year. Effects of transgenic Bt cotton on the overwintering generation of cotton bollworm appear to have significantly contributed to the suppression of cotton bollworm observed throughout northern China in the past decade. This work was published in the recent issue of  Journal of Insect Physiology (Fang Ouyang, Zhudong Liu, Jin Yin, Jianwei Su, Chenzhu Wang, Feng Ge. 2011). Effects of transgenic Bt cotton on overwintering characteristics and survival of Helicoverpa armigera (57 (2011) pp.153–160).DOI: 10.1016/j.jinsphys.2010.10.007.

The study was supported by grants from the National Basic Research Program of China (973 Program), National Nature Science Fund of China and the Special Program for new transgenic variety Breeding of the Ministry of Science and Technology, China.