Willow gall midge

The willow gall midge (Hexomyza schineri) is a specialized insect pest belonging to the order Diptera, family Agromyzidae. It is widely recognized for its ability to manipulate plant tissue development, resulting in the formation of woody galls on the stems and branches of its host plants.

The primary hosts for this species are members of the genus Salix (willow). This pest primarily impacts young saplings and ornamental willow varieties, causing significant structural damage to the stems and complicating the management of willow nurseries and ecological plantings.

The biology of Hexomyza schineri is strictly linked to the seasonal growth cycle of the host plant. Adult females oviposit into the bark of young, actively growing twigs. Upon hatching, the larva bores into the cambium and xylem tissues, triggering the plant to initiate cell proliferation around the feeding site, which forms a gall that protects the developing larva throughout its life cycle until pupation.

The damage caused by this midge manifests as spherical or oblong swellings along the stems. These galls interfere with the normal vascular function of the branch, restricting nutrient and water transport. As a result, the affected branches often become brittle, may break during wind events, and can lead to dieback of distal sections of the plant.

Effective management of this pest focuses on physical control and cultural practices, as chemical interventions are rarely effective due to the protective structure of the gall. Key control strategies include:

• Systematic pruning and removal of infested shoots before the adult emergence period.
• Proper destruction of pruned material to eliminate the reservoir of the next generation.
• Inspection and quarantine of nursery stock to prevent the introduction of the pest to new areas.
• Promotion of tree vigor through appropriate fertilization and water management to minimize the impact of colonization.