Virulence of Beauveria to Spodoptera frugiperda in western Yunnan and its dynamics in fields.
Purpose: Beauveria strain with higher virulence against Spodoptera frugiperda was screened to provide the fungal resource reserve for the ecological prevention and control of S. frugiperda; field investigation on B. bassiana was done to lay the foundation for the understanding the natural occurring situation of Beauveria in field ecosystem. Method: The virulence of 10 Beauveria species, totally 15 strains, from Baoshan City, Nujiang Prefecture and Dali Prefecture, were tested by crawling infection way. The dynamics of B. bassiana in a year in four types of field ecosystems (coffee garden, tea garden, corn field and tobacco field) in Baoshan was analyzed. Results: The virulence of 15 Beauveria strains to S. frugiperda was different. The strain with the lowest virulence caused only 10% mortality rate. There were nine strains with higher virulence causing 100% mortality rate, while their lethality speed were different, total lethal time being 4.4-15.7 days, LT50 being 2.3-10.3 days. Thereinto, the strain BUB12 from Nujiang river beach of Lujiangba in Baoshan had the highest virulence (total lethal time=4.4 d, LT50=2.3 d), and the strain BUB8 from a tobacco field of Tengchong in Baoshan had the second highest virulence (total lethal time=5.8 d, LT50=2.5 d). B. bassiana were distributed throughout the entire year in all the four types of field soil and the highest strains number was detected in summer. The quantities of B. bassiana in perennial crops fields (tea garden and coffee garden) were higher than the annual crop fields (corn field and tobacco field). Conclusion: B. bassiana strain BUM12 and BUM8 had the best virulent effect against S. frugiperda and had greater application potential.