About Rabdophaga rosaria (Loew, 1850)
The willow genus Salix is extremely susceptible to gall induction and growth manipulation, and it is one of the plant genera with the highest known number of associated gall-forming species. Rabdophaga rosaria is likely a group of closely related, still unnamed species, where each member may be restricted to a single willow species. Galls caused by this group should be recorded as R. rosaria, and the host willow species should also be recorded separately. The gall formed by this insect consists of 30 to 60 shortened, tightly packed leaves arranged in a rosette shape at the shoot tip. It forms on multiple willow species: white willow (Salix alba), crack willow (Salix fragilis), goat willow (Salix caprea), purple willow (Salix purpurea), eared sallow (Salix aurita), and grey sallow (Salix cinerea). After this species lays eggs, a chemical interaction stops the infected willow shoot from growing lengthwise. Leaves on the shoot keep developing, which forms the characteristic rose-like gall at the tip of the affected shoot. Rabdophaga rosaria forms galls on willow branches; the diameter of the gall depends on the willow species. Galls are larger on Salix caprea, reaching 8 centimetres (3.1 in), while they grow to 3 cm (1.2 in) on Salix alba. In the United Kingdom, gall development begins in May or June as leaves expand, and the galls reach maturity in August or September, when they are still green. The galls turn brown, stay on the tree through the winter, and are pushed off by new spring growth. Rabdophaga rosaria is widely distributed across the United Kingdom, where it is locally common. It is abundant in Finland.
