Invasive Vespa velutina nigrithorax hornets are more susceptible to entomopathogenic fungus than two other hymenopteran species, the wasp Vespa vulgaris and the bumblebee Bombus terrestris.
Entomopathogenic fungi are commonly used as biological control agents. Recently, a strain of Metarhizium robertsii (Sorokin, 1883) (Hypocreales: Clavicipitaceae) collected in France was identified as a good candidate for controlling invasive populations of yellow-legged hornet, Vespa velutina nigrithorax (Buysson, 1905) (Hymenoptera: Vespidae) in Europe. Since M. robertsii is generalist, its use as bioagent could be damaging for non-targeted species. Here, we compared the lethal effects of three concentrations of this M. robertsii strain on the invasive hornet and two non-targeted species commonly found in Europe, the common wasp Vespa vulgaris (Linnaeus, 1758) (Hymenoptera: Vespidae) and the buff-tailed bumblebee Bombus terrestris (Linnaeus, 1758) (Hymenoptera: Apidae). Exposure to M. robertsii spores altered the survival of all three species but at different degrees. Hornets had consistently lower survival, even under low concentrations of spores, when compared to wasps and bumblebees. Such lower susceptibility of beneficial Hymenoptera is encouraging in the perspectives of using M. robertsii as biocontrol agent against invasive hornets.