食物和温湿度对二点委夜蛾幼虫取食和为害玉米苗的影响

Effects of food, temperature and humidity on feeding of Athetis lepigone (Lepidoptera: Noctuidae) larvae and their injury to maize seedlings

【目的】调查显示,二点委夜蛾Athetis lepigone在田间的虫口密度与玉米被害率之间无明显的相关性,田间虫口密度并不能准确预测玉米苗被害率。为了探索二点委夜蛾幼虫发生量与玉米苗被害程度之间的关系,解释田间调查遇到的幼虫即使有时大量发生玉米苗却受损轻微的现象,本研究室内检测了外部环境条件如温度和湿度对二点委夜蛾幼虫取食为害玉米的影响以及昆虫自身的相关取食习性。【方法】将3龄末、4龄初二点委夜蛾幼虫分别置于下述8种温湿度和食物组合条件下进行处理:低温低湿无食物(15℃, 30%RH,饥饿)、低温干燥无食物(15℃, 0%RH,饥饿)、低温低湿有食物[15℃, 30%RH,饲喂人工饲料(AD)]、低温干燥有食物(15℃, 0%RH, AD)、高温高湿有食物(36℃, 90%RH, AD)、高温干燥有食物(36℃, 0%RH, AD)、高温高湿无食物(36℃, 90%RH,饥饿)、高温干燥无食物(36℃, 0%RH,饥饿);处理4 h后,评价其对盆栽玉米苗的为害程度,并测定幼虫在4个不同温度(15℃, 24℃, 28℃和33℃)下对玉米叶片的取食量。分别用8种食物(马齿苋、紫苏、甘薯、白菜、大豆、南瓜和玉米叶叶片以及麦秸)将初孵幼虫驯化饲喂至3龄后,检测经过驯化处理后的幼虫对初始驯化食物、麦秸和和玉米叶片的选择性。【结果】在干燥条件下,无论是否经过饥饿处理,幼虫对玉米苗的为害程度均较高,尤其是高温干燥处理后,对玉米苗的平均为害级别达3.1级;低温干燥处理组和高温干燥处理组为害级别在4级以上(含4级)的幼苗数分别占幼苗总数的50%和40%。在15-33℃,二点委夜蛾幼虫的取食量随温度的升高而逐渐增加,48 h校正取食量分别为12.8, 31.8, 38.0和60.0 mg。用甘薯、白菜、大豆和南瓜叶片驯化的幼虫对初始驯化食物的选择率显著高于对玉米和麦秸的选择率;初始取食紫苏叶片的幼虫对紫苏和麦秸的选择率显著高于对玉米的选择性,初始取食玉米叶片、麦秸的幼虫分别对玉米、麦秸的选择性更高。【结论】干燥是二点委夜蛾幼虫增加对玉米摄入量的一个主要因素;二点委夜蛾适应短时高、低温的能力较强,在一定的温度范围(15-33℃),短时间内的取食量随温度升高而增加。作为干燥的一个辅助因素,温度通过影响二点委夜蛾幼虫的取食量而决定其为害玉米苗的程度;二点委夜蛾倾向于选择初孵幼虫最先接触的食物;二点委夜蛾在玉米苗上的发生为害在很大程度上取决于其自身食性。

【Aim】 Surveyes showed that there was no correlation between the population density of Athetis lepigone larvae and the damage rate of maize seedlings, and the damage rate of maize seedlings cannot be accurately predicted according to the number of larvae in the field. In this study, the effects of environmental conditions such as temperature and humidity on the feeding and damage of A. lepigone to corn and the feeding habits of this insect were investigated in the laboratory in order to explore the relationship between the number of A. lepigone larvae and their injury to maize seedlings and to explain the phenomena encountered in the field investigations that maize seedlings are slightly damaged even though its larvae occur in large numbers.【Methods】 The damage degrees of the 3 rd and 4 th instar larvae of A. lepigone to maize seedlings were evaluated after the larvae were subjected to the following eight treatment combinations of temperature, humidity and food, respectively, for 4 h: 15℃, 30% RH and starvation(no food supplied);15℃, 0% RH and starvation;15℃, 30% RH and fed with artificial diet(AD);15℃, 0% RH and AD;36℃, 90% RH and AD;36℃, 0%RH and AD;36℃, 90%RH and starvation;and 36℃, 0% RH and starvation. The food consumption of larvae on maize leaves at four different temperatures(15℃, 24℃, 28℃ and 33℃) was measured. The newly hatched larvae were domesticated by feeding on eight kinds of food(leaves of purslane, purple perilla, sweet potato, Chinese cabbage, soybean, pumpkin and maize, and wheat straws), respectively, till the 3 rd instar, then the feeding preference of the domesticated larvae to the initial food for domestication, wheat straw and maize leaves was assayed.【Results】 The damage grades of A. lepigone larvae under drought conditions were higher whether they had experienced starvation or not;especially in the high temperature and desiccation treatment group, the average damage grade of larvae to maize seedlings reached 3.1. The percentages of injured seedlings with the damage grade above grade 4(including grade 4) were 50% and 40%, respectively, when the larvae were subjected to the low temperature and desiccation treatment and the high temperature and desiccation treatment. The feeding amount of larvae to maize leaves increased gradually with the increase of temperature between 15-33℃, with the corrected feeding amount of 12.8, 31.8, 38.0 and 60.0 mg, respectively, at 48 h after treatment. Larvae domesticated with leaves of sweet potato, cabbage, soybean and pumpkin were more likely to choose the initial food for domestication. Larvae domesticated with perilla leaves preferred perilla and wheat straw to maize leaves. Similarly, larvae domesticated with maize leaves and wheat straw had greater preference to maize leaves and wheat straw, respectively.【Conclusion】 The results show that desiccation is a major factor in increasing the intake of A. lepigone larvae to maize seedlings. A. lepigone larvae have a strong adaptability to short-term high and low temperature, and their feeding amount increases with the increase of temperature in a short time and a certain temperature range(15-33℃). Temperature as a supplementary of desiccation also affects the damage degree of the larvae to maize seedlings. In addition, A. lepigone larvae tend to choose the food they come into contact with immediately after hatching for feeding, and the occurrence and damage of this insect to maize seedlings also largely depend on its feeding habits.