Abstract The poplar twiggall fly (PTGF), Hexomyza schineri (Giraud) (Diptera: Agromyzidae), makes smoothly rounded galls on current season twigs of aspen that persist and continue to expand into large swellings years after insect emergence. Early season observations noted that adults make feeding puncture wounds in foliage with their ovipositor that are good indicators of early season activity. Oviposition in twigs results in an observable swelling of tissues within days. However, full development of galls does not occur until approximately two months following oviposition. Adults typically were active for a period of about two to three weeks subsequent to bud break and its primary parasitoid, the eurytomid Eurytoma contractura Bugbee, was trapped at the end of the PTGF flight period. Efforts to prevent adult emergence by painting galls two weeks prior to adult emergence with either sealants (shellac, polyurethane) or insecticides (imidacloprid, abamectin) did not reduce adult emergence. Soil drench treatments of imidacloprid prior to and immediately following bud break significantly reduced PTGF gall production. High rates of thiamethoxam also provided suppression of galling. Foliar applications tested were ineffective in control of gall production by this insect.