Abstract: Releasing experiments of the parasite, Trichogramma chilonis, for control of the cot ton bollworm Helicoverpa armigera were conducted in cotton fields in Yucheng, Shandong Province in 1994 and 1995. The results indicated that: the effective dispersal distance (EDD) of T. chilonis was positively related to both the length of sunshine and the average field temperature (AFT) duringthe releasing periods. When the temperature was higher than 24℃, most of the patasites dispersed beyond 25 m and when it was lower than 20.7℃, all of them distributed within 1-25 m. During June-August, their EDD varied from 10 m to 25 m. Rairffall severely influenced their EDD and parasitizing rate. EDD of the egg parasite showed a significant negative correlation with the field relative humudity (FRH), when FRH was above 89% their EDD became greatly shortened and most of them distributed near the releasing site.

Key words: Trichogramma chilonis, cotton bollworm, effective dispersal distance, weather fac- tots