Abstract: The predatory gall midge, Aphidoletes aphidimyza, is an effective natural enemy of aphids. We investigatded effects of aphid abundance on daily oviposition, lifetime fecundity, and egg hatching rate using non-choice laboratory trials. Female gall midges were individually exposed to with aphid patches designated at four levels in aphid density for oviposition. Eggs laid daily were counted and cultured for hatching. Aphid density had a strong influence on daily egg deposition and lifetime fecundity in the gall midge. Daily egg deposition decreased from 18 eggs for 3-day old females to 2 eggs for 9-day old females, but increased from 5 eggs on aphid patches with of 5 aphids/plant to 12 eggs on those with 40 aphids/plant. Lifetime fecundity increased from 18 eggs on low aphid density (5 aphids/plant) patches to 53 eggs on high density (40 aphids/plant) ones. When aphid density was less than 20 aphids/plant, egg hatching rate ranged between 70% and 90% and did not vary with midge senescence. When aphid density was 40 aphids/plant, egg hatching rate decreased with midge senescence, from 90% on the 3rd day to 33% on the 9th day. The results suggest that female A. aphidimyza can adjust its oviposition rate in response to aphid abundance, and egg hatching rate decreases with midge senescence in the case of high aphid densities.