Drosophila suzukiiandDrosophila melanogastercoexist with different but overlapping resource use in the field. When forced to completely or partially share resources in the laboratory,D. melanogasteroutcompetesD. suzukii. AdultD. suzukiiandD. melanogasterfemales were allowed to compete for access to a common oviposition resource in pairwise and population scale experiments. We tracked the offspring emergence to explore the factors across life stages that might affect the success ofD. suzukiiin the laboratory compared to a closed field simulation cage experiment with a generalistDrosophilaparasitoid,Pachycrepoideous vindemmiae. When in competition as adults,D. melanogasterproduced more offspring that survived to pupation thanD. suzukii. In addition,D. melanogasterproduced more offspring when in competition with a conspecific than when in competition withD. suzukii. Competitor identity did not affect the number ofD. melanogasteroffspring in pairwise and cage experiments. However, in the presence ofD. melanogaster, the number ofD. suzukiioffspring in both pairwise and cage experiments was dramatically reduced than in cages without this competitor. In the presence of bothD. melanogasterandP. vindemmiae, there were marginally moreD. suzukiithan when onlyD. melanogasterwas present. These results suggest that competition was an important factor limitingD. suzukiinumbers. LimitingD. suzukiinumbers through interspecies competition may eventually be an exploitable method of biocontrol in the field. [ABSTRACT FROM PUBLISHER]