华北棉区棉铃虫种群动态与其为害特征分析

本文述及棉铃虫为害特性及其与为害后棉株的补偿作用关系。根据棉株生命表资料,蕾期棉株蕾花的脱落主要系由棉铃虫为害所致。而铃期蕾铃的脱落,则主要系由棉株的生理条件。在蕾期,前三周内蕾花被害脱落后,棉株的补偿作用是很高的,从第四周起补偿作用逐渐下降,而到铃期阶段时补偿作用降至很低水平。因此蕾期棉株遭受一定数量以内的棉铃虫为害,而使蕾花脱落后,反而可促使棉花增产。根据棉铃虫生命表资料,从卵期至三龄末幼虫期的累计死亡率占总死亡率的90%以上,结合幼虫死亡率与不同龄期为害水平分析,棉铃虫对棉株的主要为害阶段系在2—3龄期,其对果实的为害量占总为害的65%。而棉株被害蕾铃的田间空间分布型系遵从负二项分布,期公共K值为3.4626。

AN ANALYSIS ON POPULATION FLUCTUATION AND DAMAGE CHARACTERISTICS OF COTTON BOLLWORM IN COTTON AREAS OF NORTH CHINA

This paper deals with the relationship between the damage characteristies of the cot-ton bollworm Hcliothis armigera and the compensatory capacity of cotton plants after ppst damage in cotton areas of North China. It is found that less than half of the squares that a cotton plant produces will form mature bolls; and in the square stage the shedding of the fruits is mainly caused by cotton bollworms while in the boll sta.ge the shedding seems to be dominantly due to the physiological condition of the plant. Therefore, in North China cotton bollworm is usually regarded as a major pest of cotton in square stage. The cotton plants show good compensatory capacity for the early loss of fruits. The compensation is usually very high in the first three weeks of the square stage, gradually diminishes from the fourth week and drops to a very low level in the boll stage. Therefore in the square stage the limited shedding of squares caused by slight, cotton bollworm damage on cotton may ironically raise the cotton yield and also improve the -quality of cotton.The life table of cotton bollworm in North China shows that the total mortality is principally decided from the egg stage to the third instar larvae during which the accumulative mortality amounts to more than 90% of the total. An analysis on larval mortality with injury levels of different instars shows that the main damage stage coincides with the second and third instars in larval development, during which the numbers of damaged fruits occupy 65% of the total. The spatial distribution of the damaged fruits on the cotton plants follows a negative binomal distribution. The common K value is 3.4626.