Determination of the larval instars of Athetis lepigone (M?schler)
Author of the article:LI Zhao-Bo1** LI Jing-Wen1 ZHAO Nan2 YU Yi1 ZHANG An-Sheng1 ZHAI Yi-Fan1 LI Li-Li1***
Author's Workplace：1. Key Laboratory for Plant Virology of Shandong, Institute of Plant Protection, Shandong Academy of Agricultural Sciences,Jinan 250100, China; 2. Laizhou Municipal Bureau of Agriculture, Laizhou 261400, China
Key Words：Athetis lepigone, stadium, head capsule width, body length, body weight
Abstract： [Objectives] Athetis lepigone (Möschler) (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=0.4579e0.2121x. Identification of instars on the basis of body length and body weight was unreliable due to the large degree of overlap in these measures.