Abstract: To understand the larval feeding pattern of the outbreak population, Loxostege sticticalis, the variation of larval food utilization parameters and digestive enzyme activity of L. sticticalis among three larval densities (1, 10 and 30 larvae/jar of 650 mL) were studied in the laboratory (22±1℃, 70% RH). The results showed that the highest and lowest midgut relative mass was found in the larvae reared at the density of 10 larvae per jar and 1 larva per jar, respectively. Larval relative consumption rate and excretion dry weight increased, but body weight and the efficiency of conversation of ingested food (ECI) declined as larval density rose. The relative consumption rate and dry weight of excretion of larvae reared at the density of 30 larvae per jar was significantly higher than that of larvae reared at the density of 1 larva per jar and 10 larvae per jar, while the ECI of larvae reared at the density of 30 larvae per jar was significantly lower than that of larvae reared at the density of 1 larva per jar. The approximate digestibility (AD) was significantly declined with increasing larval density. Furthermore, larval density had a significant influence on the activity of protease enzyme. The activity of total protease and leucine aminopeptidase enzyme was significantly higher in the larvae reared at the density of 10 than that at the densities of 1 and 30 larvae per jar, but the activity of amylase enzyme was not affected by larval density. The change trend of relative mass of larval midgut among three densities was consistent with the activity of total protease and leucine aminopeptidase enzyme. The variation of digestive enzyme activity may be relevant to the midgut relative mass. Thus, larval population density is one of the major factors affecting feeding behavior feature of L. sticticalis. These results provide evidence for clarifying the different damage feature between the outbreak and common populations.

Key words: Loxostege sticticalis, larval density, food utilization efficiency, digestive enzyme, enzyme activity