甜菜夜蛾幼虫龄数和龄期的测定

甜菜夜蛾Spodoptera exigua(Hübner)]属鳞翅目(Lepidoptera)夜蛾科(Noctuidae),是芦笋、番茄、棉花、萝卜、玉米等植物上的重要害虫。明确该虫幼虫的龄数和龄期,可为其预测预报和科学防治提供依据。对甜菜夜蛾幼虫各龄期的头壳宽度、体长和体重进行测量,并根据频次分布图、戴氏定律、Crosby生长法则和回归分析推断和验证甜菜夜蛾幼虫的虫龄数。结果显示,甜菜夜蛾1~5龄幼虫的头壳宽度范围分别为0.21~0.30、0.40~0.49、0.65~0.75、1.05~1.15、1.65~1.80 mm,频次分布呈现出5个明显的集中区域;1~5龄幼虫的体长范围分别为1.0~3.1、2.5~6.5、4.0~10.0、5.0~15.0、11.0~27.0 mm,各龄期体长出现重叠,频次分布集中区域不明显;1~5龄幼虫的体重范围分别为0.025~0.567、0.200~6.000、1.100~15.200、6.200~65.600、32.900~275.200 mg。结果表明,试验条件下甜菜夜蛾幼虫共5龄,幼虫头壳宽度可作为分龄指标,而幼虫体长和体重在各龄期出现较大程度的重叠,不宜作为分龄指标。

Determination of larval instars of Spodoptera exigua (Hübner)

Spodoptera exigua(Hübner) (Lepidoptera: Noctuidae) is a serious pest of various crops, such as asparagus, tomato, cotton, radish, corn and so on. Its damaging range is very broad in China, therefore, it is necessary to determine the larval instars, which is an important evidence for forecasting and proper control of this pest. The number of larval instars was determined and tested based on frequency distribution analysis, Dyar’s rule and Crosby’s growth rule after measuring three indexes including head capsule width, body length and body weight. It was found that the range of head capsule width from the 1^st to the 5^th instar of S. exigua was 0.21-0.30, 0.40-0.49, 0.65-0.75, 1.05-1.15, 1.65-1.80 mm, respectively, and frequency distribution analysis showed five obvious concentration areas. The range of body length from the 1^st to the 5^th instar of S. exigua was 1.0-3.1, 2.5-6.5, 4.0-10.0, 5.0-15.0, 11.0-27.0 mm, respectively, which exhibited no obvious concentration areas. The range of body weight from the 1^st to the 5^th instar of S. exigua was 0.025-0.567, 0.200-6.000, 1.100-15.200, 6.200-65.600, 32.900-275.200 mg, respectively. These results indicated that there were 5 instars for S. exigua under the experiment conditions, and the head capsule width could be applied to the identification of larval instars rather than the body length and body weight due to the overlap among instars.