Oak gall midge

Systematic position. The oak gall midge Arnoldiola quercus belongs to the order Diptera, family Cecidomyiidae. It is a specialized insect species whose life cycle is intricately linked to the development of vegetative parts of trees within the Quercus genus.

Host plants. The primary host is the English oak (Quercus robur). The pest mainly targets young leaves, causing specific tissue alterations that result in the weakening of the tree and a decline in its aesthetic and physiological health.

Biology and life cycle. Adults are small insects, and their flight period coincides with the bud break and leaf unfolding phase of the oak. Females lay eggs inside the leaf tissues. Upon hatching, larvae stimulate abnormal plant cell growth, forming galls — enclosed structures where they develop while feeding on plant sap until pupation.

Nature of damage. Due to larval activity, small galls appear on the surface of the leaves. During mass outbreaks, the leaf surface becomes densely covered with these formations, disrupting photosynthesis. This leads to premature yellowing and leaf abscission, ultimately reducing the tree's overall wood increment.

Control measures. Controlling gall midges is challenging because the larvae are protected from contact insecticides by the gall tissue. Key management practices include:

• Sanitary pruning and removal of affected branches.
• Application of systemic insecticides during the adult flight period.
• Maintaining tree vigor through proper silvicultural management.
• Encouraging natural biological control agents to keep pest populations in check.