The interactive effect of environmental stochasticity and resource driven intraspecific competition on Culex quinquefasciatus (Diptera: Culicidae) larval productivity Pubblico
Koval, Will (2017)
Abstract
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. I hypothesize that rainfall events decrease strain from exploitative intraspecific competition via the associated reduction of immature density and the introduction of detritus. To address my hypothesis, I 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 dervie 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 in the larval matrix. Generalized Linear Models of larval mortality from laboratory experiments were used as the metric for density-dependent population effects alonga 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 high density treatment (0.375 mg/larva) had the largest mortality rate at [0.0155 ± CI 0.0005 larvae/day, p << 0.001]. Depsite 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/larva). using experimentally informed metabolic ages, single and double rain event regimes were simulated and compared to a null model that did not account for competition. 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 realtes 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
Table of Contents
Abstract iiv Acknowledgements iv Glossary i Introduction 1 Study Hypothesis 7 Methods 9 In-Lab Experiments 9 Semi-Natural Observation Study 10 Statistics 11 Model Development 12 Model Analysis 17 Assumptions 17 Results 19 In-Lab Experiments 19 Model Application 20 Model Sensitivity 22 Semi-Natural Observation 23 Discussion 25 Conclusions 28 Future Directions
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References31
Tables 35Table 1. Larvicides used in urban catch basins and their measured efficacy
35Table 2.Starting nutrient availability and daily addition
36Table 3.List of metrics used in the calculation of model parameters
36Table 4.Survivorship and metamorphosis rates in larval competition experiments
37Table 5.Generalized Linear Models of mortality curves in low nutrient environments
38Table 6. Transition matrices of Models N* and A
38Table 7.Relative abundance of adult species in the Baker woods study area
39Table 8.Sensitivity analysis of Model A based on consumption rate
40 Figures 41Figure 1.The West Nile Virus Transmission Cycle
41Figure 2.A diagram of the catch basin habitat found in urban environments
42Figure 3.Methods Flow Chart
43Figure 4.Bioquip mosquito breeder diagram
44Figure 5.Container used as a mesocosm during the semi-natural observation study
45Figure 6.Diagram of a light trap courtesy of Fairfax County Health Department
46Figure 7.The matrix projection cycle
47Figure 8.The structural difference between Model N* and Model A
48Figure 9.Rates of stage change in larval competition experiments
49Figure 10.Survivorship to the next stage in larval competition experiments
50Figure 11.Mortality rates within the larval competition experiment
51Figure 12.The predicted consumption rates of the three lower nutrient treatments
52Figure 13.Predicted cumulative consumption and observed stage change
53Figure 14.A sample model run with a rain event at day 10
54Figure 15.The metabolic age distribution of a population before and after a rain event
55Figure 16.Rain delayed adult proliferation in Models N* and A
56Figure 17.Boxplots of Model A rain delay simulations
57Figure 18.Sensitivity analysis of the Model A simulation
58Figure 19.Rain delayed adult proliferation in Models B and C
59Figure 20.Semi-natural observed larval counts
60Figure 21.Curve shape from Model A and semi-natural observation
61Figure 22.Age distribution effects of rainfall and insecticide treatment
62Figure 23.Delayed proliferation and age synchrony from insecticide application
63About this Honors Thesis
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