Members of the Cx. pipiens complex (Cx. pipiens quinquefasciatus in the Southern US) play a critical role in the spillover of urban arboviruses such as West Nile Virus or St. Louis Encephalitis virus . Field studies show strong correlation between the periodicity of rainfall events and larval proliferation in the vector's primary urban habitat: roadside catch basins. However, mechanistic determinants driving this relationship have not been empirically tested. We hypothesize that rainfall events decrease strain from exploitative intraspecific competition via the associated dilution of immature individuals and introduction of detritus. To quantify the impact of rainfall on key life history parameters of Cx. quinquefasciatus, we used a deterministic matrix projection model consisting of an age-structured larval matrix coupled with a stage-structured adult mosquito matrix. Laboratory competition experiments were used to derive key model parameters, such as consumption, survivorship, and time to stage change. Consumption rate, calculated from mortality as a function of available resources, is an indirect measure used to inform the metabolic ages of the larval matrix. Once the model was calibrated with existing data, we quantified the effect of rainfall periodicity on mosquito population size and nutrient loading.
Results/Conclusions
Generalized Linear Models of larval mortality from laboratory experiments were used as the metric for density-dependent population effects along a four-level nutrient gradient (0.375, 0.75, 1.5, 3 mg fish food per capita). Density-dependent effects were observed in the lower three treatment levels. The 0.375 mg/larva treatment had the largest mortality slope at [0.0155 ± 0.0005, p << 0.001]. Despite variable time to pupation across treatments (17.07 ± CI 7.43 days), average day of metamorphosis in each treatment was associated with relatively consistent lifetime consumption (32.05 ± CI 0.07 mg). Using experimentally informed metabolic ages, model output was simulated under single and double rain event regimes. Stable, low-level population cycles were achieved after initial boom and bust dynamics in single rain event simulations. Variable rain delays in two-event simulations showed optimal proliferation occurring at a delay of 19 days between events. This is comparable to the pattern observed in natural populations, demonstrating that realistic Cx. quinquefasciatus proliferation rates can be modeled mechanistically as a density-dependent system. The empirical understanding of density-dependence as it relates to environmental stochasticity provides a theoretical platform for the study of larval dynamics and the impact of larval control in this medically relevant disease vector.