Selection of a highly virulent fungal isolate, Metarhizium anisopliae CLO 53, for controlling Hoplia philanthus

Abstract

The June beetle, Hoplia philanthus Füessly (Coleoptera: Scarabaeidae), has become a widespread and destructive insect pest of lawns, sport turf, pastures, and horticultural crops in Belgium. The virulence of 34 entomopathogenic fungal isolates from the genera Metarhizium, Beauveria, and Paecilomyces to third-instar H. philanthus was tested in bioassays by dipping larvae in 10 7 conidia/ml suspensions. Two isolates of Metarhizium anisopliae (CLO 53 and CLO 54) caused maximally 90% mortality 10 weeks post-inoculation while other isolates only caused mortalities between 10 and 62%. The virulence of M. anisopliae CLO 53 was further tested by exposing H. philanthus larvae to conidial serial concentrations of 10 4–10 9 conidia/g sandy soil for up to 11 weeks at 15, 20 or 25 °C. Mortality was dependant on the fungal concentration, exposure time, and temperature. Eleven weeks after inoculation, the LC 50 values for this isolate ranged from 1.3 to 4.0 × 10 6, 1.0 to 3.2 × 10 5, and 2.5 × 10 4 to 10 5 conidia/g soil at 15, 20, and 25 °C, respectively. The LT 50 values for this isolate ranged from 3.5 to 21.7, 2.4 to 18.7, and 2.9 to 16.1 weeks at concentrations of 10 9 and 10 4 conidia/g soil at 15, 20, and 25 °C, respectively. In glasshouse pot experiment with perennial ryegrass ( Lolium perenne L.), the isolate CLO 53 caused mortalities of 50 and 88% of H. philanthus larvae 10 weeks after application of 10 4 and 10 6 conidia/cm 2 soil surface, respectively. The present results suggest that the Belgian isolate CLO 53 has excellent potential for biological control of H. philanthus.