粘虫幼虫密度对幼虫食物利用率的影响

EFFECTS OF REARING DENSITY ON THE FOOD CONSUMPTION AND UTILIZATION OF LARVAL ORIENTAL ARMYWORM MYTHIMNA SEPARATA(WALKER)

本文对粘虫Ｍｙｔｈｉｍｎａｓｅｐａｒａｔａ（Ｗａｌｋｅｒ）不同幼虫密度下（１头／瓶、１５头／瓶、３０头／瓶）５龄至预蛹和６龄至预蛹的幼虫食物取食量、粪便排泄量、近似消化率、体重增长和粗生长效率等进行了研究。结果表明：幼虫的食物取食量、粪便排泄量随幼虫密度的增加而加大。表明群居或幼虫密度的增加可使幼虫的取食量增加从而使为害加重。但是，幼虫的体重增长则随幼虫密度的增加而下降，这是因为近似消化率和粗生长效率也随幼虫密度的增加而下降的缘故。由此认为，食物利用率下降是高密度条件下粘虫个体较小的主要原因之一。但是，这些效应均随幼虫密度影响的消失而消失。

A laboratory evaluation of food consumption and utilization by larvae of Mythimna separata (Walker) under different rearing densities (1, 15, 30 larvae/jar) was made from the beginning of the fifth and sixth instar of larvae to the prepupal stage on the corn seedling. The food consumption, whether on daily of total basis increased with the larval density increased indicating that crowding may stimulate food intake of the larvae and hence enhance their damage on crops. This trend is also conspicuous in the amount of voided faeces. The growth, as measured by daily larval fresh weight was the highest at the density of 1 larva/jar, followed by 15 and 30 larvae/jar, due to the lower efficiency of approximate digestibility (AD) and lower efficiency in converting ingested food into body matter (ECI)in the higher rearing densities. Presumably, the lower AD and ECI should be the bases of the major reasons for the smaller size of M. separata in the crowded conditions. It should, however be noted that all these difference would become insignificant as the period of larvae separating from the given rearing density become longer.