人工释放赤眼蜂对棉铃虫的防治作用及相关生态效应

1998～2000年在河北省南皮县棉区转Bt基因棉田及常规棉田中设置4种不同的组合处理，通过释放螟黄赤眼蜂控制棉铃虫的方法，减少化学农药的使用，达到提升和增强自然生物控制力的生态效应；并以不采取任何防治措施的常规棉田为常规棉对照田。研究表明：（1）转基因棉和常规棉棉田中自然寄生率随棉铃虫世代的增加而逐渐升高，2、3和4代棉铃虫卵被寄生率范围分别为13.3%～14.3%、26.7%～28.2%和60.8%～61.4%。（2）棉铃虫2代期，在常规棉综防田释放赤眼蜂2次，其寄生率为46.4%, 比未释放赤眼蜂的转基因棉棉田和常规棉对照田提高33.1%和32.1%； 3代期，转基因棉棉田释放赤眼蜂1次，其寄生率与常规棉综防田释放4次的效果相当，分别为73.7%和68.1%；但与转基因棉不放蜂田、常规棉化防田及对照田相比，分别提高45.5%、61. 8%和47.0%；4代期，无论放蜂与否，各处理棉田中的寄生率除化防田外（52.1%）均在60%以上。（3）常规棉化防田棉铃虫2代和3代期，分别使用农药2和3次，其自然寄生率分别为5.5%和11.9%，与对照田相比，分别降低8.8%和14.8%；与常规棉综防田相比，分别降低40.9%和56.2%；释放赤眼蜂的效果与施药时间有关，放蜂后1天内施药，寄生率仅为12.5%,施药后2天放蜂，寄生率达45.6%。（4）转基因棉棉田棉铃虫累计数和百株蕾铃被害数比常规棉综防田分别减少74.8%和73.8%，捕食性天敌增加63.0%；放蜂Bt棉田比不放蜂Bt棉田棉铃虫累计数、百株蕾铃被害数分别减少61.8%和33.3%；常规棉综防田棉铃虫累计数、百株蕾铃被害数、农药使用量比化防棉田分别减少29.7%、43.4%和60.0%,捕食性天敌数量增加63.0%。（5）转基因棉田和综防棉田的益害比（捕食性天敌/植食性害虫）分别为0.47∶1和0.30∶1, 而化防棉田为0.24∶1。上述结果表明释放赤眼蜂可弥补抗虫棉后期抗性减弱的不足，增加田间自然天敌的数量，提高对棉田害虫的自然控害功能。

Control of Helicoverpa armigera and related ecological effects following mass-release of Trichogramma chilonis in transgenic Bt and routine cotton fields

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.