Mediterranean Europe
Giant reed (Arundo donax)
Eggs are tiny, milky-white, and have stalk-like pedicels. Larvae are creamy-white but partially translucent and are typically 4 mm long by the third instar. Pupae are 5 mm long and are creamy-white initially but eventually turn dark. Adults are <7 mm long (not including antennae) with black, tapering bodies and brown legs. Antennae are long and brown to black, and the wings are transparent with pale yellow veins.
Adults lay eggs inside giant reed stems near shoot tips. Numerous eggs are often laid individually within the same stem. This species of wasp is able to lay eggs without fertilization, so there are very few males. Oviposition induces the formation of a gall around the deposited egg, and hatching larvae feed on gall tissue through three instars. Pupation occurs within galls. Adults chew a small, round exit hole to emerge from the gall. There may be up to five generations per year, depending on site conditions. In warm climates, wasp populations may be active year-round. In colder climates, pupae overwinter within galls, and adults emerge the following spring.
Galling likely disrupts movement of metabolites in the stem and weakens stem structure, increasing risk of breakage, especially where multiple larvae feed within stems, which can lead to distortion, breakage, and death of young main shoots and death of side shoots. High wasp populations significantly reduce live giant reed stem density, height, and biomass.
Moran, P.J. and J.A. Goolsby. 2022. Giant Reed Biocontrol Agents: History and Ecology in North America. In: R.L. Winston, Ed. Biological Control of Weeds in North America. North American Invasive Species Management Association, Milwaukee, WI. NAISMA-BCW-2022-37-GIANT REED-A. https://bugwoodcloud.org/resource/files/23209.pdf