Both adult females and larvae of Agromyza frontella (Rondani) exploit the same food source, alfalfa leaflets. In laboratory studies, larval development in leaflets with many adult nutrition holes resulted in a higher incidence of mortality than in leaflets with low levels of adult feeding. Furthermore, in heavily attacked leaflets, survivors had a slightly longer larval developmental time and lower pupal weights. In heavily attacked alfalfa fields where adult nutrition holes are numerous, the above-mentioned adult–larval interaction could play a density-dependent role in the population dynamics of A. frontella. However, in most situations adult feeding probably has an indirect effect, accentuating intraspecific larval competition by decreasing the quantity of the available limiting resource.