The interactive effect of environmental stochasticity and resource driven intraspecific competition on Culex quinquefasciatus (Diptera: Culicidae) larval productivity Open Access

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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References

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Tables 35

Table 1. Larvicides used in urban catch basins and their measured efficacy

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Table 2.Starting nutrient availability and daily addition

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Table 3.List of metrics used in the calculation of model parameters

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Table 4.Survivorship and metamorphosis rates in larval competition experiments

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Table 5.Generalized Linear Models of mortality curves in low nutrient environments

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Table 6. Transition matrices of Models N* and A

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Table 7.Relative abundance of adult species in the Baker woods study area

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Table 8.Sensitivity analysis of Model A based on consumption rate

40 Figures 41

Figure 1.The West Nile Virus Transmission Cycle

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Figure 2.A diagram of the catch basin habitat found in urban environments

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Figure 3.Methods Flow Chart

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Figure 4.Bioquip mosquito breeder diagram

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Figure 5.Container used as a mesocosm during the semi-natural observation study

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Figure 6.Diagram of a light trap courtesy of Fairfax County Health Department

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Figure 7.The matrix projection cycle

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Figure 8.The structural difference between Model N* and Model A

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Figure 9.Rates of stage change in larval competition experiments

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Figure 10.Survivorship to the next stage in larval competition experiments

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Figure 11.Mortality rates within the larval competition experiment

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Figure 12.The predicted consumption rates of the three lower nutrient treatments

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Figure 13.Predicted cumulative consumption and observed stage change

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Figure 14.A sample model run with a rain event at day 10

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Figure 15.The metabolic age distribution of a population before and after a rain event

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Figure 16.Rain delayed adult proliferation in Models N* and A

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Figure 17.Boxplots of Model A rain delay simulations

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Figure 18.Sensitivity analysis of the Model A simulation

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Figure 19.Rain delayed adult proliferation in Models B and C

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Figure 20.Semi-natural observed larval counts

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Figure 21.Curve shape from Model A and semi-natural observation

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Figure 22.Age distribution effects of rainfall and insecticide treatment

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Figure 23.Delayed proliferation and age synchrony from insecticide application

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About this Honors Thesis

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School	Emory College
Department	English and History
Degree	BS
Submission	Honors Thesis
Language	English
Research Field	Biology, Ecology
Keyword	Population Ecology Competition Culex
Committee Chair / Thesis Advisor	Vazquez Prokopec, Gonzalo, Emory University
Committee Members	Beck, Christopher, Emory University Kitron, Uriel, Emory University

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