Biological control of Strophosoma spp. (Coleoptera: Curculionidae) in greenery (Abies procera) plantations using Hyphomycetes

In Abies procera plantations Strophosoma melanogrammum and S. capitatum cause economic damage due to the adult stage feeding on the needles. No chemical treatments of these weevils are allowed in Denmark, so the potential of biological control was evaluated. We studied pathogenicity of thirteen isolates of entomopathogenic fungi and the field effect of soil application of Metarhizium anisopliae against Strophosoma spp. All of the tested isolates were capable of causing infections under laboratory conditions and average survival time at 20°C ranged between 13 and 23 days for S. melanogrammum and between 23 and 28 days for S. capitatum when dipped in a fungal suspension adjusted to 1×10⁷ conidia mL^-1. Under field conditions up to 90% of the living collected individuals died due to M. anisopliae infection in the treated plots, whereas less than 1% died of M. anisopliae infection in control plots. In accordance, the population of Strophosoma spp. was reduced in plots where the fungus was applied compared to control plots.