Indirect interactions between a native and a supposedly non-native wasp species (Hymenoptera: Vespidae: Eumeninae: Anterhynchium)

Non-native species pose a threat to native organisms. When non-native and native species are closely related, the former can often competitively exclude the latter. Many studies have focused on competitive exclusion of native insect species by non-native eusocial hymenopterans, including ants, hornets, paper wasps and bees. Although solitary species of wasps have been introduced in many regions, few studies have investigated the effects of these insects on their native congeners. We investigated competitive interactions between native and non-native solitary wasps belonging to the same genus (Hymenoptera: Vespidae: Eumeninae: Anterhynchium). Specifically, we compared resource use and natural enemies of the native Anterhynchium flavomarginatum and supposedly non-native A. gibbifrons at a forest edge in Takasago, Hyogo, Japan, in June-October 2019, using trap nests (bamboo canes). Of 950 bamboo canes, 70 (7.4%) and 50 (5.3%) were used as nests by A. flavomarginatum and A. gibbifrons, respectively. Anterhynchium flavomarginatum produced two generations over the period studied, whereas A. gibbifrons produced only one. Although A. gibbifrons began nesting two weeks after A. flavomarginatum, the nesting period of A. gibbifrons overlapped that of the first nesting period of A. flavomarginatum. Nest architecture and the inner diameter of the canes used by both species were similar, suggesting potential competition for nesting resources. Anterhynchium flavomarginatum used larvae of 14 species of moths (Lepidoptera: Crambidae, Pyralidae, Tortricidae) as food for their larval offspring, whereas A. gibbifrons used only a single species, Demobotys pervulgalis (Lepidoptera: Crambidae). Prey species were exclusive to each wasp species, indicating no competition for this resource. Three parasitoid species, Macrosiagon nasutum (Coleoptera: Ripiphoridae), Amobia distorta (Diptera: Sarcophagidae) and Megaselia sp. (Diptera: Phoridae), attacked both Anterhynchium species. The percentage parasitism by Amobia distorta was higher for the native A. flavomarginatum. Anterhynchium gibbifrons may indirectly affect A. flavomarginatum via shared parasitoids.