Promote Early Resilience Cultivated Cotton Bollworm Occurrence Of The Law And Its Chemical Control Technology

Studies on the Population Dynamic of the Cotton Bollworm and the Chemical Control Technique in Early Maturity and Adverse Resistance Cultivation Cotton Fields Abstract The effect of different cultivation of cotton on the population dynamic of the cotton bollworm, Helicoverpa armigera (I-IUbner) and the effectiveness of chemical control were studied based on the pest integrated management theory. The cultivation models of cotton can result in the change of local environment in cotton fields, which undoubtedly affects the population dynamics of the cotton bollworm and the chemical control effectiveness. The investigation was carried out in conventional cultivation and adverse resistance cultivation cotton fields with high-density and dwarf-body culture. Compared between the two cultivation models, the adverse resistance cultivation had some advantages as follows: reduced number of eggs, the postponement of the egg-laying peak and reduced the times of insecticide application, shortened egg-laying peak duration, decreased survival rate of eggs to the third instar larva and the damage rate of squares, making the distribution of eggs to be suitable for chemical control. The adverse- resistance cultivation model was suited for the special climate in Shanxi province .It was characterized by short plants, short branches and small leaves, which improved the shady condition in the fields, and making spray more easily and effectively. Investigation showed that the insecticide coverage over leaves was increased by 4.6% to 7.8%, the mortality of bollworm was increased by 4.l%to 12.3%, the total amount of cotton bollworm was decreased by 6 tol3 per 100 plants, the number of damaged squares was decreased by 50 to 150 per 100 plants. Over-wintering pupa was the important resource of the bollworm of the next year. The investigation showed that over-wintering pupa occurred in the adverse- resistance cultivation model field decreased that conventional cultivation and over- wintering pupa was distributed mainly in field mounding, where the pupa number was as 5 times as that in the middle field .The area of the mounding was only about 14% of the whole cotton field, while the pupa number in it amounted to 30%to 40%. Chemical control still played an important role in the cotton bollworm integrated management. Some insecticides screening tests, the efficacy of the chemical control by using different spraying equipment and the proper interval of insecticide application were studied.