Effects of larval density on resistance of Mythimna separata larvae to Bacillus thuringiensis and Beauveria bassiana

Author of the article:KONG Hai-Long YUAN Lin DONG Chuan-Lei ZHENG Min-Yuan JING Wang-Hui TIAN Zhen HOU Qiu-Li

Author's Workplace：College of Plant Protection and Horticulture, Yangzhou University, Yangzhou 225009, China；College of Plant Protection and Horticulture, Yangzhou University, Yangzhou 225009, China；College of Plant Protection and Horticulture, Yangzhou University, Yangzhou 225009, China；College of Plant Protection and Horticulture, Yangzhou University, Yangzhou 225009, China；College of Plant Protection and Horticulture, Yangzhou University, Yangzhou 225009, China；College of Plant Protection and Horticulture, Yangzhou University, Yangzhou 225009, China；College of Plant Protection and Horticulture, Yangzhou University, Yangzhou 225009, China

Key Words：Mythimna separata; Bacillus thuringiensis; Beauveria bassiana; larval density; disease resistance

Abstract：

[Objectives]  To clarify the dynamics of disease resistance in Mythimna separata larvae reared at different larval densities. [Methods]  The resistance of larvae to Bacillus thuringiensis (Bt) and Beauveria bassiana at densities of 1, 2, 5, 10 and 30 larvae per jar were tested by the membrane method and the immersion method in a laboratory. [Results]  Larval density had significant effects on the survival rate and survival time of larvae infected with Bt and B. bassiana. At higher larval densities the survival rate and survival time of larvae infected with Bt significantly increased. The survival rate was highest at a density of 10 larvae per jar, which was significantly higher than that at densities of 1 and 2 larvae per jar. The larval survival time was longest at a density of 30 larvae per jar, which was significantly longer than that at 1, 2 and 5 larvae per jar. The trend in survival rate and survival time of larvae infected with Bt at different densities was consistent with that of larvae infected with B. bassiana. The survival rate and survival time of larvae at high densities were significantly higher than that of larvae at low densities. [Conclusion]  Larval density has an important effect on disease resistance in M. separata; larvae have significantly greater resistance at higher than at lower densities.