草地贪夜蛾不同虫口密度对海南鲜食玉米产量的影响及其经济阈值研究

草地贪夜蛾[Spodoptera frugiperda (J. E. Smith)]在海南省可周年繁殖,世代重叠严重,常年危害海南鲜食玉米,防治困难。为了解海南省不同虫口密度草地贪夜蛾幼虫在鲜食玉米各个阶段对其产量的影响,采用田间接种不同密度3龄幼虫的方法来模拟自然危害,研究其经济阈值。结果表明,苗期（4~6叶）、喇叭口期（8~10叶）和抽穗期（12~14叶）各阶段,虫口密度与危害程度的回归方程分别为：y=0.06ln(x)+0.1258、y=0.0546ln(x)+0.1863、y=0.0589ln(x)+0.0275,计算出不影响玉米产量的危害程度分别为：21.57%、28.34%、14.50%。虫口密度与总产量在苗期（4~6叶）、喇叭口期（8~10叶）和抽穗期（12~14叶）的回归方程分别为：y=-0.2508x+13.113、y=-0.1093x+12.721、y=-0.0616x+12.447,得出不影响产量的虫口密度分别为：5头/20株、7头/20株、9头/20株;各时期的经济阈值分别为：6~8头/20株、12~20头/20株、19~24头/20株。该研究结果为海南省鲜食玉米田草地贪夜蛾的精准防治及合理的农药减量提供科学依据,对提高防治经济效益、保护生态环境等具有重要意义。

Effect of Different Population Density of Spodoptera frugiperda on the Yield of Corn and Its Economic Threshold

Spodoptera frugiperda (J. E. Smith) can propagate annually in Hainan Province and has serious overlapping generations. It harms the production of fresh corn in Hainan Province and is difficult to control. In order to understand the effects of different population densities of S. frugiperda larvae on the yield of fresh corn field in Hainan Province, the third instar larvae of S. frugiperda were inoculated in the field to simulate natural hazards and study its economic threshold. The results showed that the regression equations of population density and total yield at seedling stage (4-6 leaves), bell stage (8-10 leaves) and heading stage (12-14 leaves) were as follows: y=-0.2508x+13.113, y=-0.1093x+ 12.721 and y=-0.0616x+ 12.447. The results showed that the population density which did not affect the yield was 5, 7, 9 larvae per 20 plants. The regression equations of population density and damage degree were as follows: y=0.06ln(x)+0.1258, y=0.0546ln(x)+0.1863, y=0.0589ln(x)+0.0275. The results showed that the damage degree of corn yield was 21.57%, 28.34% and 14.50%, and the economic threshold of each period was 6-8, 12-20, 19-24 larvaes per 20 plants, respectively. The results would provide a scientific basis for the precise control and reasonable pesticide reduction of S. frugiperda in corn fields of Hainan Province, which is of great significance to improve the economic benefits of control and protect the ecological environment.