Mediterranean Europe
Giant reed (Arundo donax)
Crawlers are orange, ¼–½ mm long, and become covered with a waxy whitecap scale while feeding. A brown waxy secretion is added to the periphery of this whitecap and serves as the scale covering of the immobile second instars. Short-lived adult males are winged, orangish-brown, and just over ½ mm long. Male scales when developing are oyster-shaped, about 0.5–1.0 mm long, and often found attached to larger female scales. Adult females are more round, covered by the brown and white scale, and expand their bodies up to 2 mm in diameter while developing the next generation of crawlers.
There are two immature stages or instars of R. donacisprior to the adult stage. Mobile crawlers (first instar) emerge from the body of the adult female in winter or early spring. They disperse up to a few feet (1 m) and settle on giant reed leaf collars at the bases of side shoots and rhizomes. Once settled, they become immobile, begin feeding on giant reed tissue with their piercing/sucking mouthparts, and secrete a waxy whitecap covering. The first instars then secrete a brown waxy covering around the edges of the whitecap and molt to the immobile second instar. Male pupation occurs beneath their oyster-shaped brown scale coverings. Adult males are winged and mobile while adult females are immobile and remain beneath the waxy scale cover. Adult males find and mate with females, and then die after only 2–3 days. Females continue to develop beneath their scale covering, more than doubling their body size as they develop crawler embryos and continue feeding. The full female life cycle requires 5–6 months. There may be one or, possibly, two overlapping generations per year, depending on site conditions.
Heavy scale infestation of side shoot bases leads to a ‘witches broom’ symptom. In release plots, scale infestations combined with heavy galling by the arundo wasp (Tetramesa romana, see next section) reduce live biomass of giant reed by about 50% compared to plots with only the wasp.
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