The pathogenicity of Metarhizium anisopliae and Beauveria bassiana for adults of the Japanese beetle, Popillia japonica (Coleoptera: Scarabaeidae)

Conidia of Metarhizium anisopliae and Beauveria bassiana were evaluated for activity against adults of the Japanese beetle, Popillia japonica, under laboratory conditions. The LC50 values 7 days after exposure to M. anisopliae and B. bassiana were 0.7 and 0.026 mg of conidia/100 adults, respectively at 22-24°C. A sharp increase in mortality was observed 3 and 4 days after treatment with either 10 mg of B. bassiana/100 adults or 10 mg of M. anisopliae/100 adults, respectively. The LT50 values at 10 mg/100 beetles for M. anisopliae and B. bassiana were 4.2 and 3.1 days. respectively. Onset of mortality was further delayed at lower dosages of both fungi. Mortality of adults that were exposed to beetles treated with 10 mg of conidia of M. anisopliae/100 adults immediately following application of conidia or 24 hrs posttreatment was an average of 60 and 43% cumulative mortality. respectively, within 9 days of exposure. Similar exposures of healthy adults to beetles that had been treated with 10 mg of B. bassiana conidia/100 adults resulted in an average of 79 and 43% cumulative mortality, respectively. Beetles killed either by M. anisopliae or B. bassiana and subsequently placed on damp soil manifested signs of patent infection with the fungi, with subsequent production of conidia. The infectivity of M. anisopliae and B. bassiana for adult Japanese beetles and the delay in mortality following treatment provide potential for dispersal of these entomopathogens within populations of P. japonica.