Abstract: To understand the roles of larval density in the cellular immunity of the beet webworm, Loxostege sticticalis L. (Lepidoptera: Pyralidae), the types, number and composition of hemocytes in its 5th instar larvae reared on intact plants of Chenopodium album L. at the density of 1, 5, 10, and 20 larvae/jar (900 mL) were investigated. Five types of hemocytes were identified from larval L. sticticalis, i.e., prohemocytes, granular hemocytes, plasmatocytes, spherulocytes and oenocytoids. The numbers of plasmatocytes, granular hemocytes and total hemocytes increased as the larval density increased, but the numbers of prohemocytes, spherulocytes, and oenocytoids were insignificantly affected by the larval density. The proportion of each hemocyte type to the total haemocetes ranked in a similar order in the four treatments but the ratios of plasmatocytes at the density of 10 and 20 larvae/jar were remarkably higher than that of the isolated larvae. These results suggest that the larval density can affect the number of plasmatocytes and granular hemocytes, and this impact in turn can affect the cellular immune capacity in larval L. sticticalis.

Key words: Loxostege sticticalis, larval density, hemocytes, cellular immunity, plasmatocytes, granular hemocytes