Abstract:  To investigate the effects of larval density on the population growth of the beet webworm, Loxostege sticticalis, the larval duration and survival, pupal weight and adult fecundity were examined by rearing larvae at the densities of 1， 10， 20， 30 and 40 larvae/650 mL jar under laboratory conditions (22±1℃, RH 70%±5%, photoperiod 16L∶ 8D). The results showed that larval cuticular color, developmental duration and survival, pupal weight and adult fecundity of L. sticticalis were significantly affected by larval density. Larval cuticular melanization score became greater as the density increased, and the scores at the densities exceeding 10 larvae per jar were significantly higher than that at the density of one larva per jar (P<0.05). The developmental time of larva and pupa at the density of 20 larvae per jar was the shortest, while it was significantly prolonged as the larval density increased (P<0.05). The larval survival rate was the highest at the density of 10 larvae per jar, which was significantly higher than those at other densities (P<0.05). Pupal weight was the heaviest at the density of one larva per jar, and it was significantly reduced with the increase of larval density. The total fecundity per female and the proportion of mating individuals were the highest at the density of one larva and 20 larvae per jar, respectively, and they decreased as larval density increased. Adult oviposition duration was gradually shortened with the increase of larval density. The longevity of female and male was the longest at the density of 10 and 20 larvae per jar, respectively, while it was significantly shortened when larval density was too high. Life table analysis indicated that the population growth index was significantly affected by larval density, and it was the highest at the density of 10 larvae per jar, but lower at either higher or lower density. It is so concluded that larval density is one of the major factors influencing population growth in L. sticticalis.

Key words: Loxostege sticticalis, larval density, growth, development, reproduction, life table, population growth index