麦田接种释放中华草蛉成活率的研究

1986～1987年在河北省定州市进行了小麦田接种释放中华草蛉的试验。麦收时调查,33％的茧结在麦株顶部,67％的茧结在植株下部枯黄叶上和土缝中。在4月28日、5月10日和5月17日释放草蛉1龄幼虫,6月12日麦收时结茧率分別为27％、53.5％和36.3％,以5月10日释放的成活率最高。茧的羽化率则随释放期的延迟而减少,分别为100％、67％和23％。麦收时尚未羽化的茧,在麦秸处理和耕种措施中将遭到破坏。麦田草蛉羽化后转移到棉花、玉米等夏作上,因此在麦田中能安全羽化的草蛉数(成虫获得率),将影响夏作上草蛉的基数。综合考虑结茧率和羽化率,认为适期(约麦收前一个月)在麦田接种释放,结茧率(53.5％)和成虫获得率(35.8％)均较高,对小麦和夏作上草蛉的成活和增殖最为有利。在430亩小麦上接种释放草蛉,6月上旬放蛉区内玉米上的草蛉成虫密度较不放蛉区玉米上明显增加。在马铃薯、苜蓿和菜豆地释放草蛉,成活率均较小麦上为低。

FIELD STUDIES ON THE SURVIVAL OF CHRYSOPERLA S1NICA [NEU.:CHRYSOPIDAE] MASS REARED AND INOCULATIVELY RELEASED IN WHEAT FIELDS IN NORTHERN CHINA

The significance of Chrysoperla sinica, a predominant native predator, in controlling pests of cotton, corn and vegetables in Northern. China is often hampered by its low populations in the early season. To develop new strategies of increasing the lacewing population, field experiments on inoculative release of mass reared C. sinica in wheat fields in late spring-early summer were conducted in Dingzhou, Hebei Province during 1986-1987. Investigations at the harvest of wheat showed that 33% of the cocoons, of C. sinica was on tips of the wheat plants, while 67% was attached on the lower dried leaves and in ground crevices. Releases of the first instar larvae on April 28, May 10 and May 17 resulted in 27%, 53.5% and 36.3% pupation rates, respectively, by the time of wheat harvest. The adult emergence rates of these pupae were 100%, 67% and 23%, respectively. Delayed releases resulted in reduction of the adult emergence rate. It was found that unemerged cocoons by the harvest were mostly damaged by processing of wheat straw and tillage and seeding practices. Adults emerged from the wheat field dispersed on to cotton, corn, and other summer crops after the harvest. The number of safely emerged adults from the wheat field would influence the initial population number of the lacewings on the summer crops. Thus, the optimal timing for the release was determined to be one month prior to wheat harvest, or mid-May. Release of C. sinica in 430 mu of wheat fields resulted in a significant increase in the adult numbers on corn in the releasing area, compared with that in the non-releasing area. The survival rates of the lacewings released in fields of potato, alfalfa, or vegetable beans were all significantly lower than that released in wheat fields.