Epizootiology of Amblyospora stimuli (Microsporidiida : Amblyosporidae) infections in field populations of a univoltine mosquito, Aedes stimulans (Diptera : Culicidae), inhabiting a temporary vernal pool

The epizootiology of the microsporidium Amblyospora stimuli was studied in natural populations of a univoltine mosquito, Aedes stimulans, inhabiting a temporary vernal pool over an 18-year period. The yearly prevalence of ben ign oenocytic infections in adult females was variable, ranging from 1.0 to 9.6% (mean = 5.1%). The yearly prevalence of transovarially transmitted me iospore infections in larval populations was consistently lower but less va riable, ranging from 1.3 to 5.9% (mean = 3.5%). Meiospore infections in F-1 -generation larvae were significantly correlated with infections in parenta l-generation females, thus suggesting that larval infection rates could be substantially increased if methods were available to facilitate transmissio n of A. stimuli to a larger portion of the female population via inundative or inoculative release of infected copepods. No correlation was found when infections in filial-generation adult females were measured against meiosp ore infections in larvae from the preceding year. Analysis of yearly preval ence data using Fine's Fundamental Vertical Transmission Equation revealed low rates of horizontal transmission from the intermediate copepod host to female larvae in most years, ranging from 0.1 to 8.7% (mean = 3.1%). A stim uli is enzootic, persists at a very low level, and has minimal impact on Ae . stimulans populations at this site. The low incidence rate of horizontal transmission to larvae appears to be due largely to a paucity of copepods a nd is a major factor that limits the abundance and subsequent proliferation of A. stimuli in Ae. stimulans populations at this locale. Results support the view that host-parasite cospeciation is an important mechanism of evol ution in this group of mosquito/copepod microsporidia. (C) 1999 Academic Pr ess.