Evidence for the copepods Acanthocyclops robustus and Mesocyclops edax as competent intermediate hosts for Coelomomyces punctatus during an epizootic in a larval population of the mosquito Anopheles quadrimaculatus.

Field and laboratory experiments were conducted during an epizootic of Coelomomyces punctatus (Chytridiomycetes: Blastocladiales) in a population of the mosquito Anopheles quadrimaculatus in a North Carolina farm pond to examine the interactions of several potential copepod hosts with the mosquito and fungus. The diel vertical migratory behavior of the copepod species Acanthocyclops robustus, Eucyclops serrulatus, Macrocyclops albidus, and Mesocyclops edax were monitored in relation to infection rates in sentinel mosquito larvae. Mosquito infection occurred primarily around dusk, the same period during which A. robustus and E. serrulatus were most abundant near the surface of the pond. However, exposure of A. robustus, E. serrulatus, M. albidus, M. edax, Microcyclops varicans, and Paracyclops poppei to fungal meiospores in the laboratory showed that only A. robustus and M. edax were competent intermediate hosts for C. punctatus. Laboratory studies of the diel periodicity of gametangial dehiscence in A. robustus and M. edax infected with C. punctatus revealed that gamete release and zygote formation also occurred around dusk. The combined results of the laboratory and field studies on copepod abundance, susceptibility to infection, and periodicity of gametangial dehiscence suggest that A. robustus was the principal intermediate host for C. punctatus during the epizootic, though it is probable that M. edax also contributed importantly to the overall rate of larval infection.