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.