Effects of four plant populations and intercropping beans with maize on the population patterns of bean flies (Ophiomyia phaseoliTryon,O. centrosematisde Meijere, andMelanagromyza spencerellaGreathead) on common beans were studied. Percentage of plants infested by bean flies was significantly less in the one-third beans and two-thirds maize intercrop combination than in pure stand beans. The incidence of bean flies decreased with increasing plant populations from 66,666 to 533,332 plants per ha. Ovipunctures made by bean flies in the leaves of beans were not significantly different among the various treatments. A significant and gradual decrease in the number of ovipunctures from lower to higher plant populations was recorded. The bean fly larva–pupal counts were significantly lower in both intercrop combinations than in pure stand beans; larval–pupal counts were significantly lower in higher plant populations in 1983 season. Possible reasons for population patterns of bean flies are discussed.