中文摘要：

为弄清榆木蠹蛾Holcocerus vicarius Walker幼虫的发育情况及预测其发生时间,通过测量榆木蠹蛾幼虫的头壳宽、体长、体宽、前胸背板宽、上颚长和上颚宽,运用Crosby生长法则和线性回归方法分析来找出判定幼虫龄数的最佳形态指标,推断其幼虫的龄数。结果表明：各龄幼虫头壳宽平均值的变异系数和Crosby指数最小,其他5项指标的变异系数和Crosby指数较大,头壳宽为最佳分龄指标。根据头壳宽将榆木蠹蛾幼虫分为20龄,不同龄幼虫头壳宽值符合Dyar定律提出的幼虫头壳宽增长规律,头壳宽和龄数的回归方程为y=0.233＋1.686x＋0.127x2-0.005x3（R2=0.996）。榆木蠹蛾幼虫龄数的确定为研究其发生规律、生物学习性及进行综合防治提供依据。

英文摘要：

In order to reveal the development of the carpenter moth Holcocerus vicarius（Walker） larva and forecast its occurrence time,the head capsule width,body length,body width,pronotum width,mandible length and mandible width were measured,and Crosby law and linear regression analysis were used to choose the optimal morphological index for determining the larval instars of H.vicarius.The results showed that the head capsule width provided the best index to divide instars,since its mean coefficient of variation and Crosby ratio were the least,while those of other indexes were greater.H.vicarius was determined to have twenty instars.Different instars conformed to the growth regularity of larval head capsule width proposed in Dyar＇s law.The linear regression equation of the head capsule width against the instar number was：y=0.233＋1.686x＋0.127x2-0.005x3（R2=0.996）.Determination of the larval instar number of this moth could provide the basis for studying its occurrence and biological characteristics,and facilitate to develop comprehensive prevention and control.