Willow gall midge

The genus Hexomyza belongs to the family Agromyzidae (leaf-mining flies) within the order Diptera. Unlike most related species that mine leaves, these insects are specialized gall-formers that create pathological swellings on the stems and branches of woody trees and shrubs.

The primary hosts for these pests are plants within the Salicaceae family, particularly willows and poplars. Because the larvae reside and feed entirely within the woody tissues of the host plant, they remain protected from many standard environmental factors and external control measures.

The biology of Hexomyza is closely tied to the host plant's phenology. Adults deposit eggs into the bark of young shoots. Upon hatching, the larvae initiate the formation of a gall, a tumor-like structure that serves as both a food source and a protective enclosure during the larval and pupal stages.

The damage is characterized by distinct, often knotty or elongated swellings on the branches. These galls disrupt the vascular system of the shoots, leading to stunted growth, dieback of distal parts of the branch, and an overall reduction in the structural integrity and aesthetic value of the tree.

Effective management strategies for Hexomyza focus on cultural and chemical interventions:

• Physical removal and destruction of infested branches before adult flies emerge from the galls.
• Application of systemic insecticides during the peak egg-laying period to prevent initial infestation.
• Monitoring of nursery stock to ensure that no infested materials are introduced into new areas.
• Maintaining healthy growth conditions to help trees recover from minor infestations.