Abstract: Based on two years field trials, the morphological resistance of cotton lines to cotton bollworm Helicoverpa armigera (Htibner) were analysed. The results showed that the three indices, namely, the accumulated eggs, mean larval number and damagedsquare+boll number/100 plants, in the plots of cotton lines having red leaf, okra leaf, and frego bract were decreased by 28.1%, 31.45% and 36.0%; 19.0%, 25.4% and 28.4%; and 25.8%, 32.9% and 34.0% in comparison with the check plots, respectively. The larval number and damage of square and boll of those possessing high oil glanddensity, I.e. rich in terpenoid contents, were 45.1% and 51. 4% lower than the check plots ,respectively. There were coordinated action in those having both okra and red leaf, red leaf and frego bract or glabrous leaf and denser oil gland number characters, and thethree indices of these combinations were 48.3%, 55.2% and 57. 9%;52. 7%, 58.3% and 60.6%; and 29.9%, 54. 9% and 58. 3% lower than the checks respectively. The F₁ hybrids of the check separately crossed with red, okra or glabrous leaf lines had kept their own resistance to cotton bollworm in various degrees, while the bract of F1 crossed with frego leaf line turned normal and no resistance expressed. Possibly owing to the narrow condition of plot, the cotton lines without (outside flower) nectary glands did not show resistance.

Key words: cotton, cotton bollworm, resistance to insect