Native European ants can discourage host colonization and reduce reproductive success of the invasive ambrosia beetle Xylosandrus compactus

Due to their ubiquity and their nature as generalist predators, ants have long been used as biological control agents in forest and agricultural systems. Several exotic ambrosia beetles (Coleoptera: Curculionidae: Scolytinae, Platypodinae) are considered emerging widespread pests of various trees and shrubs growing in forests, nurseries, orchards, and urban areas. Among them, the Scolytinae Xylosandrus compactus (Eichhoff) is an invasive fungus-farming species native to Asia and able to cause serious damage to a broad range of natural and cultivated plants worldwide, exerting significant ecological and economic costs. Its biology makes conventional control strategies often ineffective, while little is known about natural enemies. We explored the potential of native European predators as natural enemy of this pest, conducting laboratory tests with four widespread ant species using chestnut and laurel as beetle hosts. In particular, we evaluated the interactions between X. compactus and four species of native Euro-Mediterranean ants that usually forage on plants: Crematogaster scutellaris (Olivier), Tapinoma magnum Mayr, Temnothorax affinis (Mayr), and Temnothorax mediterraneus Ward, Brady, Fisher & Schultz. Results indicate that ants may significantly limit the reproductive success of X. compactus, increasing the mortality of the beetle foundresses and reducing their offspring. Smaller ant species may also invade X. compactus nests, killing larvae, pupae and adults, while female beetles avoid nesting in twigs previously visited by ants. These results encourage to explore possible applications of ants in the biological control of X. compactus and the ecological implications of these interactions in the field.