Willow gall sawfly

Taxonomic position. The genus Euura is a group of insects within the order Hymenoptera and the family Tenthredinidae. These sawflies are recognized for their intimate association with Salix species, as they induce the formation of galls, which serve as both protection and a food source for their larvae.

Host plants and damage. The primary hosts for these pests are willow trees. The damage is localized where larvae feed, causing the plant to produce abnormal tissue structures known as galls. These structures can be found on leaves, leaf stalks, or developing twigs, effectively creating a nutrient sink that diverts vital resources away from the tree's normal growth processes.

Biology and life cycle. The life cycle typically begins in early spring when adults emerge. After mating, females deposit eggs into plant tissue. The larval stage is spent inside the developing gall, which protects them from predators and environmental extremes. Depending on the species, pupation may occur within the gall itself or in the soil near the base of the tree during winter.

Economic and aesthetic impact. While often not lethal to mature trees, heavy infestations can cause significant aesthetic damage, making them unsuitable for landscaping or nursery sales. Young trees are particularly vulnerable; chronic gall formation can lead to stunted growth, reduced vigour, and susceptibility to other secondary diseases or stressors.

Control measures. Integrated pest management (IPM) is recommended to control Euura populations:

• Manual removal and destruction of galls early in the season to reduce the next generation.
• Application of systemic insecticides when adults are active or larvae are first hatching.
• Encouraging natural predators such as parasitic wasps that naturally regulate sawfly populations.
• Maintaining tree health through proper watering and fertilization to ensure the host can withstand minor damage.