Effectiveness of entomopathogenic fungal strains against poplar/willow weevil (Cryptorhynchus lapathi L.) larvae

The poplar and willow weevil , Cryptorhynchus lapathi L., a major universally destructive wood-boring insect has become one of the important quarantine pests that is extremely destructive to forestry development and needs to be controlled. Entomopathogenic fungi (EPF) are considered safe and friendly for humans and the environment and play important roles in controlling insect pest populations. In this study, the screening of entomopathogenic fungi for control of C. lapathi is reported through the evaluation of virulence of four fungal Beauveria bassiana (CFCC81428, CFCC83116, CFCC83486, CFCC87297) strains, one B. brongniartii (CFCC83487) strain and one Metarhizium anisopliae (CFCC88953) strain. The virulence of the different strains was appraised by correct mortality rate, cumulative mortality rate, median lethal concentration (LC 50 ) and median lethal time (LT 50 ). B. bassiana strains CFCC81428 and CFCC83116 were the most virulent among the six strains with a mortality up to 100%, and the LT 50 were 2.7 and 3.1 days. Five conidia concentrations of three strains (CFCC81428, CFCC83116 and CFCC87298) that caused high virulence was screened for dose-relationship. Their effect on controlling C. lapathi larvae were also determined under field condition by brushing conidia suspensions on C. lapathi larvae infested in a poplar trunk. The cumulative rate in the field was lower than those obtained from the laboratory, but the order of the virulence of different strains did not change. Mortality in all three strains occurred at their highest concentration (1.0 × 10 8 conidia mL −1 ). Under field conditions, the CFCC81428 strain was the most effective, causing mortalities of 80.3% and 75.2% in two plots in Beipiao and Lindian counties, respectively, followed by CFCC83116 (69.1%, 66.6%) and CFCC87298 (60.7%, 59.3%). Based on our results, the B. bassiana strain CFCC81428 has the potential as a biological insecticide to control C. lapathi larvae.