Evidence indicates low levels of hybridization in nature between the apple maggot (AM), Rhagoletis pomonella (Walsh), and snowberry maggot (SB), Rhagoletis zephyria Snow, sibling species in the R. pomonella complex. We determined the effects of AM and SB pairings on mating frequencies and production of hybrid offspring in the laboratory. Mating frequency was lowest in SB female × AM male pairings, higher in AM female × SB male and AM female × AM male pairings, and highest in SB female × SB male pairings. A greater percentage of AM female × AM male pairs produced offspring (puparia) than did AM female × SB male and SB female × AM male pairs, and a greater percentage of AM female × SB male pairs produced puparia than did SB female × AM male pairs. Male or female F1 hybrids backcrossed with AM males and with other F1 hybrids were fertile. Results suggest most R. pomonella × R. zephyria hybrids found in nature are the result of R. zephyria males mating with R. pomonella females, with few from reciprocal matings. If true, this asymmetry could lower the incidence of hybridization in nature.