Wormwood gall fly

Urophora stigma is a species of fruit fly belonging to the family Tephritidae in the order Diptera. These insects are known as gall-formers and are specifically adapted to thrive within the tissues of host plants, predominantly various species of the genus Artemisia (wormwood).

The host range is primarily limited to wormwood species. The larvae feed on the developing flower heads, inducing the plant to produce a gall—a structured protective growth that provides both nutrition and shelter for the developing larvae throughout their growth stages.

The life cycle of this fly is synchronized with the blooming period of its host. Adult flies emerge, mate, and lay eggs inside the floral buds. The larvae hatch and bore into the receptacle, where they consume tissues, leading to the characteristic gall formation. Pupation typically occurs within the gall, and the insect overwinters in this stage.

The damage caused by Urophora stigma is mainly reproductive. By consuming the inner parts of the flower heads and distorting the floral structure, the larvae prevent the production of viable seeds. While this is primarily an issue for wild plant population dynamics, it can affect efforts to manage weeds in agricultural landscapes.

Effective management and control measures focus on breaking the lifecycle. These include:

• Physical removal and destruction of infested plant stalks after the flowering season.
• Mowing of wormwood stands before the adult emergence period.
• Field sanitation to eliminate overwintering sites for the larvae.