幼虫密度对草地螟食物利用率及消化酶活性的影响

为了阐明草地螟Loxostege sticticalis大发生种群幼虫取食行为特征， 在室内条件下（温度22±1℃， 相对湿度70%）对不同幼虫密度［1， 10， 30头/瓶（650 mL）］饲养草地螟幼虫的食物利用率及消化酶活性进行了研究。结果表明： 幼虫中等（或高）密度对草地螟幼虫相对中肠重量、 相对取食量、 粪便干重、 食物利用率和近似消化率及总蛋白酶和亮氨酸氨肽酶活性影响显著。幼虫相对中肠重量以10头/瓶的幼虫密度最大， 1头/瓶的幼虫密度最小。随着幼虫密度的增加， 幼虫相对取食量和粪便干重增加， 而虫体干重减轻， 幼虫食物利用率降低。幼虫密度30头/瓶的幼虫相对取食量和粪便干重显著高于1和10头/瓶的， 而30头/瓶的幼虫食物利用率显著低于1头/瓶的。幼虫近似消化率随幼虫密度的逐渐增加而显著降低。幼虫密度10头/瓶的幼虫总蛋白酶和亮氨酸氨肽酶的活性显著高于1和30头/瓶的， 而淀粉酶的活性受幼虫密度影响不显著。随幼虫密度的增加， 幼虫相对中肠重量与总蛋白酶和亮氨酸氨肽酶活性变化趋势较为一致， 消化酶活性的变化可能与相对中肠重量大小有关。因此， 幼虫密度是影响草地螟幼虫取食行为的重要因子， 这些结果为阐明草地螟大发生种群与一般种群的为害特征提供了重要理论依据。

Effects of larval density on food utilization efficiency and digestive enzyme activity of the beet webworm,Loxostege sticticalis(Lepidoptera:Pyralidae)

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.