华北棉区第三代棉铃虫对棉花为害损失与经济阈值的研究

通过在华北棉区棉花蕾铃期阶段，连续５ａ的田间蕾铃脱落原因的观察，明确了在第三代棉铃虫的中常发生年份，影响蕾铃期蕾铃脱落的主要因素是棉株本身的自然脱落其脱落率占总脱落的９０％以上，而因第三代棉铃虫为害造成的脱落率在５％以上。根据田间棉铃虫Ｈｅｌｉｃｏｖｅｒｐａ ａｒｍｉｇｅｒａ（ｈｕｂｎｅｒ）３龄幼虫虫量与为害力的关系研究，结合多年第三代棉铃虫田间生命表，文中提出了三代棉铃虫的经济阈值为百株累计卵量

DAMAGE TO COTTON AND ECONOMIC THRESHOLD OF THIRD GENERATION COTTON BOLL WORM IN NORTHERN CHINA COTTON AREA

Observations were carried out for exploring the factors causing field shedding of reproductive organs of cotton at square boll stage in Northern China cotton areas through a successive five years period. The results show that more than 90% of the squares and young bolls fallen off from cotton plants in this stage were due to physiological shedding, and only less than 5% of the shedding was caused by the damage of 3rd generation cotton bollworm (CBW) Helicoverpa armigera (Hubner). Based on the researches on the relationship between the 3rd instar larvae number and their damage capability, combined with the analysis of natural population life table of 3rd generation CBW, the economic threshold of 3rd generation CBW was suggested as 150 accumulated egg number/100 plants.