BIOLOGY: Gall flies are very small and look similar to a tiny mosquito. Adults are difficult to find and are better identified by the gall formation on plants. Adults emerge in early spring around April – May. They lay eggs on stems. Microscopic larvae hatch in stems to form webby terminal galls. Gall midges undergo many generations per year. They emerge as a new generation every two weeks throughout the summer.

DESTRUCTIVE STAGE: Larvae (galls in stems)

IMPACT TO HOST: Gall formation can impact plants by reducing resources to kill plants. It is still too early to determine overall impact to Russian knapweed. However, early results show high establishment and distribution rates of insects. Galls can reduce flowering. Early data shows 20% reduction to Russian knapweed stands.

REDISTRIBUTION: Collect galls infested with larvae in June – August. Hatch gall wasps in lab or quarantine and collect adult midges for redistribution into the field.