Competitive effects of a recently invading wasp species on a native congener in the presence of native ants

When native and non-native congeners use the same resource, non-natives can competitively exclude natives. To clarify the effects of native ants on competitive interactions between native and non-native congeners, we experimentally investigated interactions between a native wasp species, Anterhynchium flavomarginatum , and a recently invading congener, Anterhynchium gibbifrons (Hymenoptera: Vespidae), using control and ant-excluded trap nests in central Japan. A total of 48 trap nests (12 bamboo canes per trap nest) were placed at forest edges between June and October 2021. Ants, which are native predators and nest-site competitors of Anterhynchium wasps, were experimentally excluded from half of the trap nests using a sticky barrier. Out of 288 control and 288 ant-excluded bamboo canes, A . flavomarginatum nested in 5.6% and 9.0%, respectively, producing 43 and 75 brood cells. In contrast, A . gibbifrons nested in 46.2% and 51.7%, producing 438 and 562 brood cells, respectively. The number of brood cells of A . flavomarginatum was negatively associated with that of A . gibbifrons at both the trap nest and bamboo cane levels, suggesting exploitative competition for nesting sites. Ant exclusion and other nesting insects did not significantly influence the number of brood cells of either species, suggesting that native ants do not appear to affect competitive interactions. However, ant exclusion significantly increased the survival (emergence) of A . flavomarginatum in brood cells, but not that of A . gibbifrons . Therefore, the recently invading A . gibbifrons may negatively affect the native congener A . flavomarginatum via competition for nesting resources and may be less affected by native ants.