幼虫密度对甜菜夜蛾生长发育与繁殖的影响

为了研究甜菜夜蛾Spodoptera exigua(Hübner)幼虫的密度对其发育及繁殖的影响，本实验观察了5种幼虫密度下（1，5，10，20，30头/瓶），幼虫发育和成虫繁殖情况。结果表明：幼虫和蛹历期、存活率和蛹重均差异显著。幼虫和蛹历期均以20头/瓶的最短，1头/瓶的最长，其余随幼虫密度增加而延长；幼虫至蛹存活率以10头/瓶的最高，其余随幼虫密度增加而降低；1头/瓶的蛹最重，显著高于其他密度的，其余随幼虫密度增加而下降。尽管密度间成虫羽化率和产卵前期均无显著差异，但成虫产卵量、寿命和畸形率差异显著。1头/瓶的产卵量最多，其次为10头/瓶的，其余随幼虫密度增加而减少，30头/瓶的产卵量显著少于其他密度的； 密度在1～20头/瓶范围内，雌蛾寿命均较短，显著短于30头/瓶的，而雄蛾寿命以5头/瓶的最短，显著短于其他密度的（10头/瓶除外），10头/瓶的次之，其余密度间差异不显著；不同幼虫密度下羽化的成虫畸形率差异显著，10头/瓶的最低，其余随幼虫密度增加而升高； 生命表结果表明甜菜夜蛾在10头/瓶下世代存活率和种群增长指数均最高，幼虫密度过低或过高均不利于种群增长；世代存活率（S）和种群增长指数（I）与幼虫密度之间的关系均呈抛物线关系：S =－0.2087x²+2.5694x+211.52 (R²=0.88)，I=－0.0552x²+0.9166x+54.168 (R²=0.95)。结果提示幼虫密度影响甜菜夜蛾种群动态的重要生态因子之一。

Effect of larval rearing density on development and fecundity of the beet armyworm, Spodoptera exigua (Lepidoptera: Noctuidae)

To investigate the effect of larval density on post-embryonic development and adult reproduction of Spodoptera exigua,we conducted a laboratory experiment in which larvae were reared at different larval densities(1,5,10,20 and 30 larvae/jar).The larval and pupal developmental time,survival and pupal weight were significantly different.Individuals reared at the density of 20 larvae/jar showed the shortest larval and pupal developmental time,while the longest larval and pupal developmental time occured in individuals under isolated conditions(1 larva/jar).In other rearing conditions,both larval and pupal developmental time increased with the larval density increasing.The survival rate from larvae to pupae was the highest at the density of 10 larvae/jar,while it decreased with the larval density increasing.Pupal weight was significantly different and negatively correlated to larval rearing densities.Although there were no significant differences in the eclosion rate and female pre-oviposition period at different larval rearing densities,the number of eggs laid per female,longevity and the abnormality rate of adults were significantly different.Life table analysis at five different larval rearing densities indicated that the density of 10 larvae/jar was optimal for population growth and survival,while either lower or higher densities were not.The relationship between generation survival rate(S),population growth index(I) and larval rearing density could be descried as parabola equations:S=-0.2087x2 2.5694x 211.52(R2=0.88),I=-0.0552x2 0.9166x 54.168(R2=0.95).The results suggest that larval density is one of the major ecological factors for Spodoptera exigua population dynamics.