Comparative virulence of the fungus Lecanicillium muscarium and two entomopathogenic nematodes against adult truffle beetles ( Leiodes cinnamomeus ) at low temperatures

Abstract The truffle beetle, Leiodes cinnamomeus , is the most important pest in black truffle ( Tuber melanosporum ) plantations during autumn and winter. Entomopathogenic nematodes (EPNs) are promising biological control agents against L. cinnamomeus , while entomopathogenic fungi (EPF) are also commonly used in Integrated Pest Management (IPM) programmes to enhance the control of insect pests. Our aims were to test the virulence of a cold-adapted commercial strain of the EPF Lecanicillium muscarium Ve6 and two EPN species, Steinernema carpocapsae and Steinernema feltiae , against adults of L. cinnamomeus at 15 °C and 10 °C, and to assess the effect of their combined application. Two susceptibility assays were performed using different treatments: (1) immersion of adults in a fungal suspension and (2) direct soil treatment of the EPF. Mortality of L. cinnamomeus was recorded 7 days post-treatment at 15 °C and 15 days post-treatment at 10 °C. Lecanicillium muscarium did not cause significant mortality of L. cinnamomeus . Steinernema feltiae did not cause significant mortality at 15 °C after 7 days but resulted in a statistically significant low mortality (33.3%) at 10 °C after 15 days compared to the control. Steinernema carpocapsae caused the highest mortality rates (63.3–100%) at both temperatures, suggesting it would be the best option to control adults of L. cinnamomeus in field applications. The addition of L. muscarium , did not enhance pest suppression compared to EPNs alone. To optimise IPM strategies for L. cinnamomeus control, further research is recommended to explore potential synergistic effects of combining EPNs with other cold-adapted EPF.