Species Identification of Beauveria brongniartii Strain JG-17 and Virulence Against Three Scarabaeoidae Pests

Based on the current situation of the wide variety and serious damage of scarabs, and the urgent demand of agriculture for biological control with eco-friendly and sustainable management, the virulence of Beauveria brongniartii strain JG-17 to the larvae and adults of three important scarabs in China was studied in order to provide excellent microbial resources for the research and development of scarabs biological control agents.

A high virulence fungus strain was isolated from the infected adult scarab cadavers by spore dilution method and re-inoculation experiment. The taxonomic status of strain JG-17 was determined by morphology and rDNA-ITS gene sequence analysis. The growth rate and sporulation of strain JG-17 at different culture temperatures were measured by cross method and hemocytometer method. The virulence of strain JG-17 to the adults and larvae of Holotrichia oblita, Holotrichia parallela and Anomala corpulenta was determined by immersion method and the control efficacy against the 2nd instar larvae of H. parallela was determined by peanut pot experiment.

A strain of Beauveria JG-17, which caused high virulence against adults and larvae of three scarabs, was isolated from the naturally infected scarabs adult. Strain JG-17 was identified as B. brongniartii combined with the morphological and molecular identification results. 25-29 ℃ is the optimal growth temperature for strain JG-17, and the growth rate is greater than 4 mm·d^-1. The growth rate and sporulation of strain JG-17 are the highest at 27 ℃. The cumulative mortality at 13 d of the adults of H. oblita, A. corpulenta and H. parallela treated with 1×10⁸ spores/mL of strain JG-17 spore suspension was 78.0%, 100.0% and 86.0% with the LT₅₀ values of 9.458, 6.911 and 8.391 d, respectively. At the same treatment concentration, the virulence of JG-17 to the larvae of H. parallela was higher than that of A. corpulenta and H. oblita. At the 1×10⁸ spores/mL of JG-17 concentration treatment, the cumulative mortality at 13 d of the 1st instar larvae of H. oblita, A. corpulenta and H. parallela was 76.7%, 96.7% and 100.0%, respectively, and that of the 2nd instar larvae was 66.7%, 36.7% and 100.0%, respectively. Under different spore concentrations of JG-17 treatment, the LT₅₀ of JG-17 against the 1st and 2nd instar larvae of H. parallela was significantly lower than that of A. corpulenta and H. oblita. In the pot experiment, there was no significant difference in larvae mortality between spraying evenly around the root and the furrow application with same spore dosage during the inter-tillage period, and more than 10 times of spore were needed to achieve similar control efficacy with spreading application before sowing.

B. brongniartii JG-17 has a high lethality rate to the adults and larvae of H. oblita, H. parallela and A. corpulenta. It is a biocontrol microbial resource with great potential for development and application to control underground scarab pests.