东方木蠹蛾幼虫龄期划分及形态判别指标筛选

Instar classification and selection of optimal morphological discriminant traits for Cossus orientalis larvae

摘要

【目的】东方木蠹蛾是我国重要的林木蛀干害虫，对甘肃河西走廊地区的二白杨和旱柳等防护林树种造成严重危害。因其幼虫钻蛀取食，世代长且不整齐，虫龄精准判定较为困难，明确幼虫龄数及最佳分龄指标是实现精准预测与科学防控的重要依据。【方法】于 2023 年 7 月 8 日至 2025 年 9 月 18 日在甘肃省嘉峪关市样地共获得不同龄期东方木蠹蛾幼虫 2 139 头，通过野外采集并结合室内饲养，系统测定东方木蠹蛾幼虫头壳宽、上颚长、上颚宽、体长、体宽和前胸背板宽 6 项形态指标，运用频次分布法和 Dyar 定律初步判断幼虫龄数，并利用 Crosby 生长法则和回归模型对各项指标的龄数判别进行交叉验证与评估。【结果】在东方木蠹蛾幼虫的 6 项形态指标中，头壳宽、上颚长、上颚宽和前胸背板宽的频次分布均呈现出 19 个聚集峰值（离散峰），体长的频次分布有 18 个离散峰，体宽有 20 个离散峰，其中头壳宽、上颚长和上颚宽的变异系数均低于 20%，Crosby 指数均低于 10%，符合 Crosby 生长法则，可作为分龄指标，因此，可确定东方木蠹蛾幼虫为 19 龄。回归分析显示三次模型与东方木蠹蛾幼虫分龄拟合效果最佳，头壳宽与龄数拟合度最高，决定系数最大（R² = 0.997 1），且 Crosby 指数和变异系数均最低，为幼虫最佳分龄指标。【结论】研究发现河西走廊地区东方木蠹蛾的幼虫为 19 龄，头壳宽为幼虫龄数判别的最佳指标。本研究弥补了该虫龄数判别量化标准的不足，为发生规律研究与监测防控提供了依据。

Abstract

[Objective] The carpenter mothCossus orientalis is an important wood-boring pest of forest trees in China, which causes severe damage to shelterbelt tree species such as Populus × xiaohei var. gansuensis and Salix matsudana in the Hexi Corridor of Gansu Province. Its larvae bore into trunks for feeding, with a long and asynchronous life cycle, leading to considerable difficulty in the precise determination of larval instars. Clarifying the number of larval instars and identifying the optimal indicators for instar discrimination serve as an important basis to realize accurate forecasting and scientific pest management. [Method] A total of 2 139 larvae of theCossus orientalis at different developmental stages were collected from sampling plots in Jiayuguan City, Gansu Province, from July 8, 2023 to September 18, 2025. Through field sampling combined with indoor rearing, six morphological indicators of C. orientalis larvae were systematically measured, including head capsule width, mandibular length, mandibular width, body length, body width, and pronotum width. Frequency distribution analysis and Dyar’s law were used to preliminarily determine the larval instars, and Crosby’s growth rule together with regression models were applied to cross-validate and evaluate the instar determination performance of each indicator. [Result] Among the six morphological indicators ofC. orientalis larvae, the frequency distributions of head capsule width, mandibular length, mandibular width, and pronotum width each showed 19 aggregation peaks (distinct peaks), while body length and body width showed 18 and 20 distinct peaks, respectively. The coefficients of variation of head capsule width, mandibular length, and mandibular width were all below 20%, and the Crosby indices were all below 10%, which conform to Crosby’s growth rule and can therefore be used as instar determination indicators. Based on these results, the larvae of C. orientalis were determined to have 19 instars. Regression analysis showed that the cubic model provided the best fit for larval instar determination, with head capsule width showing the highest goodness of fit with instar, the largest coefficient of determination (R² = 0.997 1), and the lowest Crosby index and coefficient of variation, indicating that it is the optimal indicator for larval instar determination. [Conclusion] This study demonstrated thatC. orientalis larvae in the Hexi Corridor region undergo 19 instars, and that head capsule width is the optimal indicator for larval instar determination. This study makes up for the deficiency in quantitative criteria for larval instar discrimination of this insect, and provides a basis for research on its occurrence regularity, monitoring and control.

关键词

东方木蠹蛾 / 幼虫龄数 / 分龄指标 / Crosby 生长法则 / 拟合回归模型

Key words

Cossus orientalis / larval instar / instar indicators / Crosby’s growth rule / regression models

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基金资助

嘉峪关市重点研发计划(24-23、25-28)

国家自然科学基金项目(32501666)