Pathogenicity of microorganisms isolated from the oak platypodid, Platypus quercivorus (Murayama) (Coleoptera: Platypodidae)

Abstract

The oak platypodid, Platypus quercivorus (Murayama), is the most destructive pest of Quercus and related fagaceous species in Japan. To find an effective biocontrol agent, we determined the effectiveness of entomopathogenic microorganisms against P. quercivorus. P. quercivorus-infested Oak (Quercus serrata, Q. crispula and Q. acutissima) logs were obtained from various regions in Japan, and 28 isolates of microorganisms were isolated from P. quercivorus larvae from those logs. Using molecular methods, the microbes were then classified into 18 species. After a bioassay, we found that three fungi, Lecanicillium sp., Isaria tenuipes, Beauveria bassiana, and the bacterium Serratia marcescens had the greatest potential as biological control agents against P. quercivorus. Another bioassay was then performed to determine the effect of spore or cell densities on the pathogenicity of the four microorganisms, and optimum spore or cell densities for the microbes were determined to be 106 and 107/ml. Based on the results and other criteria, we tentatively selected B. bassiana as the best candidate for future use against P. quercivorus larvae.