Simulation of the dynamics of a microsporidian pathogen of mosquitoes

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 benign oenocytic infections in adult females was variable, ranging from 1.0 to 9.6% (mean = 5.1%). The yearly prevalence of transovarially transmitted meiospore infections in larval populations was consistently lower but less variable, ranging from 1.3 to 5.9% (mean = 3.5%). Meiospore infections in F(1)-generation larvae were significantly correlated with infections in parental-generation females, thus suggesting that larval infection rates could be substantially increased if methods were available to facilitate transmission 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 meiospore infections in larvae from the preceding year. Analysis of yearly prevalence 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. stimuli 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 and 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 evolution in this group of mosquito/copepod microsporidia.

Insect-pathogen dynamics: stage-specific susceptibility and insect density dependence

The control of insect pests by using insect pathogens as dynamic biological control agents is a recent effort. Model studies on insect-pathogen relations can help in the development of biocontrol programs. Except for the work of Briggs and Godfray [1], insect-pathogen models ignore the stage-specific susceptibility of insects. Moreover most models do not incorporate insect self-regulation. We develop stage-structured models of insect-pathogen relations incorporating insect-density dependence and disease transmitted through direct contact between susceptible and infective individuals. The models are analyzed by using steady-state and stability analysis. Numerical solutions are used as sources of further insight into the dynamics of the insect-pathogen systems. It is shown that there are major differences in the dynamics of adult- and juvenile-infecting diseases. Moreover, the interplay between insect-density dependence and stage-specific susceptibility has important consequences for the dynamics of insect-pathogen systems.