MERMITHID PARASITES OF BLACKFLIES.

Mermithid nematodes parasitize invertebrates only. A general account is given of their parasitism and the consequent mortality of blackflies. The author begins with a review of records of mermithid and blackfly association from different parts of the world and comments on the global distribution of the parasite. He discusses the life-histories of the parasites, stressing their adaptations to the moving environment of the aquatic stages of the blackfly and to the aerial environment of the adult. It is noted that the parasite usually kills its host upon emergence and has a restricted host range. Mermithids must be considered as selective mortality factors against blackfly populations. A survey of European and North American literature leads to conclusions concerning the role of the parasite in the natural regulation of blackflies. The possibility of utilizing these nematodes as biological control agents is discussed.