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The braconid wasp, <i>Diachasmimorpha longicaudata</i> (Ashmead), was introduced in Kenya from Hawaii for classical biological control of the invasive tephritid, <i>Bactrocera dorsalis</i> Hendel. Following reports that <i>D. longicaudata</i> had formed new associations with <i>Ceratitis cosyra</i>, laboratory experiments were conducted to assess the interaction between the introduced and the native parasitoid of <i>C. cosyra</i>; <i>Psyttalia cosyrae</i> (Wilkinson) under three scenarios: <i>B. dorsalis</i> only, <i>C. cosyra</i> only and mixed populations of the two species. Parasitoids were introduced to the host as sole, sequential and simultaneous releases. Host searching and probing events were five times higher for <i>D. longicaudata</i> than <i>P. cosyrae</i> with both hosts. Total parasitism was highest (78%) when <i>D. longicaudata</i> was released alone on <i>C. cosyra</i>, compared to 20% for <i>P. cosyrae</i> released on the same host. Releases of <i>P. cosyrae</i> on <i>B. dorsalis</i> resulted in 0% parasitism, compared to 64% parasitism by <i>D. longicaudata</i>. Specific parasitism for <i>P. cosyrae</i> was three times higher when <i>P. cosyrae</i> was released first in sequential releases on <i>C. cosyra</i> compared to when it was released after <i>D. longicaudata</i>. These findings suggest that the two parasitoids can both suppress <i>C. cosyra</i> but <i>B. dorsalis</i> acts as a reproductive sink for <i>P. cosyrae</i>. Our findings should form the basis of field investigations where options are much wider for both parasitoids.