Abstract: To understand the ecological effects of mass-releasing Trichogramma chilonis in cotton fields, the biological control effects of this parasite were examined in two transgenic Bt cotton fields: one in which T. chilonis had been released and one in which it had not; and three non-transgenic cotton fields: one in which T. chilonis had been released in conjunction with chemical pesticides (IPM field), one with chemical pesticides only (chemically controlled field), and a natural control field as the control (no T. chilonis release or pesticides), in Nanpi County, Hebei Province, 1998－2000. The results show that: (1) natural parasitism in both types of cotton fields gradually increased from 13.3%－14.3% in the second generation to 26.7%－28.2% in the third generation and 60.8%－61.4% in the fourth generation. (2) In the IPM field, a second release of T. chilonis achieved a parasitism rate in the second generation of the cotton bollworms of 46.4%, an increase of 33.1% and 32.1%, compared to the non-release transgenic Bt and pesticide fields. In the transgenic Bt cotton field in which T. chilonis had been released, parasitism of the third generation of cotton bollworms reached 73.7%, similar to that in the IPM field and an increase of 45.5%, 61.8% and 47.0%, respectively, compared to the nonrelease transgenic field, and the pesticide and control fields. Parasitism of the fourth generation of cotton bollworms was, except for the pesticide field (52.1%), in excess of 60.0% in all other fields. (3) Parasitism in the pesticide field was 5.5% in the second generation and 11.9% in the third generation, a decrease of 8.8% and 14.8%, compared to the transgenic field in which T. chilonis had been released, and 40.9% and 56.2% compared to the IPM field. Releasing T. chilonis one day before using insecticides was associated with a parasitism rate of just 12.5%, while releasing T. chilonis two days after using insecticides was associated with parasitism rates of up to 45.6%. (4) Compared to the IPM field, the total number of cotton bollworm larval and buds and bolls injured per 100 plants in the pesticide field decreased by 74.8% and 73.8%, the total number of predators increased by 63.0%. The total number of cotton bollworm larval, and buds and bolls injured in the transgenic Bt cotton field in which T. chilonis was released decreased by 61.8% and 33.3%, compared to the non-release transgenic Bt field. Compared to the pesticide field, the total number of cotton bollworm larval, buds and bolls injured, and the use of insecticide in the IPM field, decreased by 29.7%, 43.4% and 60.0%, while the total number of predators increased by 63.0%. (5) The ratio of predators/phytophagous pests was 0.47 in the non-release transgenic Bt field, 0.30 in the IPM field, 0.24 in the pesticide field. The above results indicate that mass-release of T. chilonis can greatly enhance control of the cotton bollworm in both transgenic and non-transgenic cotton fields.

Key words: Helicoverpa armigera, Trichogramma chilonis, transgenic Bt cotton, control role