Laboratory studies showed that the insect growth regulator Altosid 5E, applied at doses ranging from 5 to 50ppb did not interfere with the preparasitic, parasitic or postparasitic development of Romanomermis culicivorax, a Mermithid parasite of mosquitoes. Both Altosid 5E and R. culicivorax were separately effective in controlling pupal and larval populations respectively of Aedes aegypti. Host mortality was considerably increased when the Mermithid and the insect growth regulator were used concurrently against mosquitoes, suggesting a promising future for integrated mosquito control programs based on the use of Mermithids and insect juvenile hormone analogs.