二点委夜蛾幼虫虫龄的测定

Determination of the larval instars of Athetis lepigone(Mschler)

【目的】二点委夜蛾Athetis lepigone（Moschler），属鳞翅目夜蛾科。我国于2005年7月在河北省夏玉米田首次发现。近年来，该虫发生范围不断扩大，为害日益加重，因此应制定科学有效的防治策略。幼虫的虫龄和龄期测定是害虫预测预报以及制定科学防治策略的重要依据。【方法】本文通过测量二点委夜蛾幼虫头壳宽度、体长、体重，对幼虫虫龄的划分进行了研究。根据所测数据的频次分布图及Dyar定律推测幼虫虫龄数，并运用Crosby生长法则和线性回归的方法进行验证。【结果】经测量，幼虫头壳宽度值呈现出5个明显的集中区，1—5龄幼虫头壳宽度分别为0．50～0．62、0．64～0．76、0．82～0．94、1．00～1．12、1．24—1．40mm。幼虫体长呈现出4个较明显的集中区，分别为2．00～6．50、7．50～12．50、14．50～17．50、18．50—23．00mm。而实际观察测得l一5龄幼虫体长范围分别为1．96～3．60、2．78～4．10、3．98～6．20、5．38～12．48、14．06～22．96mm。1～5龄幼虫体重范围分别为〈0．0001、0．0003～0．0009、0．0005～0．0036、0．0027—0．0240、0．0337～0．1332g。【结论】研究结果表明，幼虫头壳宽度可用于分龄，二点委夜蛾幼虫期共分为5龄。头壳宽度y与幼虫虫龄x的回归方程为y=0．4579e 0.2121x。幼虫体长和体重在各龄间重叠度较大，不宜用于幼虫虫龄的划分。

[Objectives] Athetis lepigone （Moschler） （Lepidoptera： Noctuidae） was first discovered in China in a summer maize field in Hebei Province in 2005 July. The range of A. lepigone in China has expanded in recent years and the species is causing progressively more damage. Development of scientific control strategy for this pest is therefore timely. Determination of the larval instars and stadia is an important foundation for pest forecasting and the development of an effective control strategy. [Methods] Instars of A. lepigone were studied by measuring head capsule width, body length and body weight. A frequency distribution analysis and the Dyar＇s rule were used to determine the number of larval instars, which was tested using Crosby＇s growth rule and linear regression. [Results] We found that the larvae of A. lepigone could separated by head capsule width into 5 instars, and that the range of head capsule width from the 1st to 5th instar was 0.50-0.62, 0.64-0.76, 0.82-0.94, 1.00-1.12, and 1.24-1.40 mm, respectively. Larvae could be separated into 4 groups on the basis of body length, the range of each group being 2.00-6.50, 7.50-12.50, 14.50-17.50, and 18.50-23.00 mm. However, our practical observations indicate that the larval body length of the 1st to 5th instar ranged from 1.96-3.60, 2.78-4.10, 3.98-6.20, 5.38-12.48, and 14.06-22.96 mm, respectively. The range of larvae body weight from the 1st to 5th instar was 〈0.0001, 0.0003-0.0009, 0.0005-0,0036, 0.0027-0.0240, and 0.0337-0.1332 g. [Conclusion] The results indicate that head capsule width can be used for the separation of instars, and that the larvae of A. lepigone have 5 instars. The relationship between head capsule width （y） and instar （x） can be described by the linear regression equation： y=0.4579e 0.2121x. Identification of instars on the basis of body length and body weight was unreliable due to the large degree of overlap in these measures.