江苏丰县甜菜夜蛾田间种群虫源性质分析

Analysis on the population status of the beet armyworm, Spodoptera exigua (Hübner) in Fengxian, Jiangsu Province, China

通过观察甜菜夜蛾雌蛾的卵巢形态和结构变化 ,将其卵巢发育进度分为五级 ,即乳白透明期 ( )、卵黄沉积期 ( )、成熟待产期 ( )、产卵盛期 ( )和产卵末期 ( )。气候资料分析表明 ,甜菜夜蛾在江苏丰县越冬存活率极低 ,个别年份甚至不能越冬。根据当地积温预测的发蛾期远远迟于黑光灯灯下见蛾期 ,表明初上灯蛾是外来迁入虫源。以卵巢解剖法对 2 0 0 2年江苏丰县田间种群虫源性质的研究表明 ,2、3代雌虫的交配率均在 80 %左右 , 级以上卵巢比例均高于 70 % ;而 4代甜菜夜蛾的交配率为 6 4 .80 % , 级卵巢比例为 4 5 .6 6 % ,再结合当地的发蛾特征 ,可知当年 2、3代甜菜夜蛾主要以外地迁入为主 ,4代主要以本地虫源为主。根据 1 998年以来历年发蛾特征的分析 。

The beet armyworm, Spodoptera exigua (Hübner), is a polyphagous pest with worldwide distribution in tropical and subtropical regions. A number of investigations have demonstrated that this species is a strong migrant, and in temperate areas, the initiation of outbreaks by immigrants has been well documented. In recent years, the beet armyworm has risen to the status of an economically important pest of many kinds of crop in China. It has become a problem especially in the north of the country, even though this species cannot survive the cold winters typically in that region. In order to improve forecasting of the inter- and intra-annual population fluctuations of this species, the status of field populations in Fengxian County (34.79°N, 116.57°E), Jiangsu Province, was studied during 2002 by winter climatic analysis, simulation of spring emergence of the overwintered generation, light trap monitoring, field population survey and ovarian dissecting of the light trap catches. Historical light-trap data for this site, extending back to 1998, were also included in the analysis. Beet armyworm adult populations were monitored with a 20-W black-light light trap operated from early April to late October. All females trapped were dissected and graded according to the development status of their ovaries, and their mating status noted. Laboratory populations were used to develop the grading scale, using images obtained with an SMZ-143 digital dissecting microscope and enhanced with Cg2000 image-processing software. Five development grades were recognized: transparent (pupae less than 5 days old), vitellogenesis (late pupae and newly emerged moths), matured (2^(nd) and 3^(rd) day after emergence), egg-laying (4^(th) and 5^(th) day after emergence), and late egg-laying (6^(th) day after emergence, and later).The pattern of moth occurrenced indicates that four generations occurred at this location in 2002. Analysis of winter climatic data for Fengxian showed that the survival rate of overwintering pupae would be very low, possibly zero. There was a large gap between the emergence time predicted by degree-day analysis and the first light-trap catches, which strongly suggested that the moths appearing early in the season (April) were immigrants. Mating rates and the proportion of matured ovaries in the 2nd and 3rd generation (July and August) were about 80% and more than 70% respectively, but fell to 65% and 54% in the 4th generation (late-August-October). This suggests that the 2nd and 3rd generations were predominantly immigrants in 2002, but that the 4th generation mainly emerged locally.