NATIVE RANGE: East Asia (China)

FIRST FINDING IN SLOVENIA: 2007

PATHWAYS: transported with saplings and branches for grafting

POSSIBLE TO FIND: year-round

FLIGHT SEASON OF ADULTS: May-July

DESCRIPTION: A black gall wasp, up to 3 mm long, with orange legs. Only parthenogenetic females are known in this species. In early summer, these lay eggs on buds, and the larvae that hatch start feeding on the plant tissue. The following spring (March–April) the larvae resume their activity and provoke the formation of galls on the newly growing leaves. These galls are ovate, 5–20 mm long, green or sometimes slightly reddish. Between May and July, adult wasps emerge from the galls, through circular exit holes. Because of the galls, the growth of twigs, development of flowers and the fruiting of the host trees are impaired.

HABITAT: Host plants are various species of chestnuts (Castanea spp.). The wasp can be found in forests and other natural habitats, in tree nurseries, plantations and in urban areas.

STATUS: Widespread in several European countries, including in Slovenia. Rapidly spreading.

SIMILAR SPECIES: Various other species of gall wasps are very similar, but none of them occur on chestnuts.

SOURCE: Field Guide to Invasive Alien Species in European Forests