Poplar twiggall fly

Examine poplar and aspen twigs for smooth, elongated swellings on current season growth; these galls develop over two months following egg-laying. Inside each gall live greenish-yellow maggots that will eventually produce small dark flies about 1/6 inch long. In Western Washington, these galls become visible by mid to late summer, creating a gnarled appearance on affected branches.

Poplar twiggall fly completes one generation per year, with larvae pupating inside galls in late winter and adults emerging with new growth. Prune out heavily galled branches if appearance matters on ornamental trees; the pest rarely weakens vigorous poplars significantly. No chemical control is typically warranted since damage is mainly aesthetic and alternate hosts are uncommon in our region.