基于外部形态特征量化分析判别菱角水螟幼虫龄期

Using quantitative analysis of external morphological characteristics to distinguish larval instars of Parapoynx crisonalis(Walker)(Lepidoptera: Crambidae)

【目的】本实验拟为田间准确快速判别菱角水螟Parapoynx crisonalis（Walker）幼虫龄期提供一种新方法,以便监测其发生规律、预测其发生时间。【方法】本研究通过对幼虫头壳宽、复眼距、体宽和体长4项外部形态指标的测量,运用Crosby生长法则和线性回归分析方法,结合各项指标的频次分布进行分析。【结果】各龄幼虫头壳宽平均值的变异系数和Crosby指数最小,为判别幼虫龄期的最佳分龄指标,幼虫期共分为5龄,1-5龄的头壳宽分别为（0.2493±0.0053）、（0.3454±0.0018）、（0.5079±0.0031）、（0.7419±0.0190）和（1.1287±0.0369）mm,其与龄期数呈线性关系。通过实验室饲养观察菱角水螟幼虫蜕皮次数验证该虫幼虫期分为5个龄期。【结论】头壳宽为判定菱角水螟幼虫龄期的最佳指标,复眼距次之。

[Objectives] To establish a method to determine the larval instars of Parapoynx crisonalis（Walker, 1859） and thereby improve the accuracy of monitoring this pest in the field. [Methods] Four larval morphological variables, including head capsule width, distance between the compound eyes, body width, and body length, were measured. Based on frequency analysis and frequency histograms, Crosby＇s law and linear regression analysis were used to choose the best morphological criteria for distinguishing larval instars. [Results] Head capsule width was the optimal criterion for distinguishing instars, since its mean coefficient of variation and Crosby ratio were the smaller than all other indices. On this basis, P. crisonalis has five instars. The average head capsule widths of 1st to 5th instar larvae were（0.2493±0.0053）,（0.3454±0.0018）,（0.5079± 0.0031）,（0.7419±0.0190） and（1.1287±0.0369） mm, respectively. [Conclusion] Head capsule width is the best morphological criterion for distinguishing the instars of P. crisonalis, followed by the distance between the compound eyes.