Nine species of mosquitoes and several species of non-target aquatic organisms were tested for susceptibility to the mernaithid nematode, Strelkovimerrais spiculatus. All species of Anopheles, Aedes, Culex, and Toxorhynchites exposed to S. spieulatus were susceptible. Of the nine mosquito species tested, C. pipiens quinquefasciatus had the greatest tolerance to initial invasion and the highest percent infection of those that survived. High levels of infection were also achieved with Aedes taeniorhynchus and A. albopictus, but these mosquitoes were significantly less tolerant to parasitism than C. pipiens quinquefasciatus. Strelkovimermis spiculatus did not infect or develop in any of the non-target hosts tested. Key words: Aedes aegypti, Aedes albopictus, Aedes taeniorhynchus, Aedes triseriatus, Anopheles albimanus, Anopheles quadrimaculatus, biological control, Chironomus sp., Copepoda, Corethrella brakeleyi, Corixidae, Culicidae, Culex pipiens quinquefasciatus, Culex restuans, Diptera, Dytiscidae, entomopathogenic nematodes, Ephydridae, host range, Mermithidae, mosquito, nematode, Odonata, non-target organisms, safety testing, Strelkovimermis spiculatus, Toxorhynchites rutilus septentrionalis.