【目的】 本研究旨在建立红树植物榄李的重要害虫——木麻黄胸枯叶蛾Streblote castanea各虫态外部形态精准、高效的鉴定方法，并构建基于头壳宽度的幼虫龄期判别体系，以期为该害虫的快速识别、发生动态与危害程度监测、发生规律探究、预测预报及防治策略制定提供科学依据。【方法】 采用肉眼观察与高清数码摄影相结合的方法，系统观察并记录木麻黄胸枯叶蛾各虫态（卵、幼虫、蛹、成虫）的外部形态特征；使用游标卡尺测量各龄期幼虫的头壳宽度，并运用频次分布分析、Dyar法则、Brooks指数和Crosby指数及回归分析等多种统计方法，对幼虫头壳宽度数据进行分析。【结果】 木麻黄胸枯叶蛾卵呈宽椭圆形，表面光滑且具深褐色斑纹。1龄幼虫头壳深黑色且具光泽，中、后胸背部橙黄色；2龄幼虫与3龄幼虫形态相似，头壳被有灰色绒毛；4龄幼虫体呈白色、灰色和红褐色等颜色分化；5龄幼虫形态与4龄幼虫相似；6龄幼虫腹部背板具“V”形深色斑纹。蛹外被黑褐色刺毛茧。雌性成虫体型大于雄性。尽管5龄幼虫头壳宽度变化不符合Crosby生长法则，但其相邻龄期之间的头壳宽度差异均达到显著水平（P＜0.05），且头壳宽度与龄期之间具有较高的相关性（R²=0.958 2），综合头壳宽度骨化程度高、变幅分界明显、变异系数小等特征，表明头壳宽度可作为木麻黄胸枯叶蛾幼虫龄期快速判别的可靠指标（1龄约为0.97 mm，2龄约为1.55 mm，3龄约为2.32 mm，4龄约为3.39 mm，5龄约为4.35 mm，6龄约为5.39 mm）。【结论】 基于上述各虫态外部形态学特征，可在野外实现对木麻黄胸枯叶蛾的快速准确鉴定；结合幼虫头壳宽度测量数据，可高效、精准判别幼虫龄期。本研究为木麻黄胸枯叶蛾的实时监测、发生期预测及针对性防治措施的制定提供了重要的基础数据与技术支撑。

This study aims to establish accurate and efficient methods for identifying the external morphologicacharacteristics of all life stages of Streblote castanea, a pest of the mangrove plant Lumnitzera littorea, and to develop a larval instar determination system based on head capsule width. The findings are expected to provide a scientific basis for rapid pest identification, monitoring of infestation dynamics and damage severity, investigation of occurrence patterns prediction of occurrence trends, and development of control strategies. [Methods]  The external morphological features of each life stage (egg, larva, pupa, and adult) of S. castanea were systematically observed and recorded using visual inspection combined with high-definition digital photography. The head capsule width of larvae at each instar was measured with a vernier caliper. Multiple statistical methods, including frequency distribution analysis, Dyar’s rule, Brooks’ index, Crosby’s index, and regression analysis, were applied to analyze the larval head capsule width data. [Results]  The eggs are broadly oval with a smooth surface and dark brown patches. 1st-instar larvae possess a deep black, glossy head capsule and an orange-yellow dorsum on the mesothorax and metathorax. 2nd- and 3rd-instar larvae are morphologically similar, with head capsules covered by gray pubescence. 4th-instar larvae exhibit color differentiation, appearing in white, gray, and reddish-brown. 5th-instar larvae are generally similar in shape to fourth-instar larvae. 6th-instar larvae are distinguished by a dark “V”-shaped marking on the abdominal tergites. The pupae are encased in a cocoon covered with dark brown setae. Female adults are larger than males. Despite not conforming to Crosby’s growth rule, the head capsule width of 5th-instar larvae exhibited significant differences between adjacent instars (P < 0.05) and a high coefficient of determination (R²= 0.958 2). Combined with its strong sclerotization, distinct size variation boundaries, and low coefficient of variation, head capsule width serves as a reliable indicator for rapid larval instar discrimination. (1st instar: approximately 0.97 mm; 2nd instar: approximately 1.55 mm; 3rd instar: approximately 2.32 mm; 4th instar: approximately 3.39 mm; 5th instar: approximately 4.35 mm; 6th instar: approximately 5.39 mm). [Conclusion]  The external morphological characteristics described herein allow for rapid and accurate field identification of S. castanea at different life stages. Moreover, larval head capsule width measurements enable efficient and precise instar determination. This study provides essential baseline data and technical support for real-time monitoring, prediction of occurrence periods, and the development of targeted control measures against this pest.