Ecological Dynamics of Aedes aegypti-Wolbachia pipientis wAlbB Strain Interactions Restricted; Files Only

Juan Sebastian Duran Ahumada (Fall 2024)

Permanent URL: https://etd.library.emory.edu/concern/etds/2j62s6300?locale=en
Published

Abstract

Control of Aedes aegypti (vector of dengue, Zika, and chikungunya) faces challenges including insecticide resistance, vector range expansion, and emergence/re-emergence of Aedes-borne diseases. A breakthrough in vector control is the transfer of the intracellular bacteria Wolbachia into A. aegypti. Wolbachia Population Replacement (WPR), the self-sustaining biocontrol technique aims to increase the frequencies of pathogen-blocking, maternally transmitted (MT) strains that also cause cytoplasmic incompatibility (CI) to decrease vector competence of mosquito populations. Increased temperature has been shown to lead to loss of Wolbachia and CI, and that increased larval competition negatively affects the fitness and performance of Wolbachia-carrying A. aegypti. Few studies have assessed the interaction of the bacteria with combinations of abiotic factors (i.e., temperature and larval density) and the resulting impact on mosquito fitness and performance, CI induction, or Wolbachia stability.

To address gaps relevant to the functioning of wAlbB strain-based WPR for the control of A. aegypti, I 1) experimentally evaluated the individual and combined effects of larval density and temperature on fitness and performance of mosquitoes carrying the wAlbB strain in A. aegypti, 2) compared population dynamics of wAlbB-carrying and uninfected semi-field intradomicile populations, and 3) adapted a model of the influence of density-dependent demographic traits in the invasion dynamics of Wolbachia to understand their implications for wAlbB introgression dynamics.

Chapter two examines the impacts of fluctuating temperature and different initial larval density on the changes in wAlbB relative densities and wAlbB mediated mosquito fitness and performance. Differential effects of treatments across sexes and life stages of A. aegypti were found, along with changes in wAlbB titers.

Chapter three demonstrates the lack of effect of wAlbB on population dynamics of A. aegypti developing at different larval densities under semi-field conditions. Adults in the experiment had increased wAlbB relative densities and reduced frequency of wAlbB at the end of the experiment.

In chapter four, I apply an established model for Wolbachia-mediated density-dependent demographic traits to ultimately understand their implications in wAlbB invasion at the city block-level provided some of the previous findings. wAlbB delayed density-dependent larval development, hindered wAlbB’s introgression and can potentially inform WPR operational decisions.

Table of Contents

Chapter 1. Introduction         

1.1 The yellow-fever mosquito: Aedes aegypti (Linnaeus, 1762)       

Figure 1.1. Modeled fundamental niche of the yellow-fever mosquito Aedes aegypti.         

Figure 1.2. Global dengue fever occurrence.             

1.2 Control of Aedes aegypti           

Figure 1.3. Mosquito life cycle and control methods: summary of traditional and new methods, emphasis on interventions focused on mosquito reproductive biology.    

1.3 Wolbachia pipientis strains in the control of A. aegypti      

Figure 1.4. Incompatible Insect Technique (IIT) and Wolbachia population replacement (WPR) in the control of Aedes aegypti: reproductive manipulation and Wolbachia-induced phenomena.        

1.4 Dissertation Overview   

Chapter 2. Wolbachia pipientis (Rickettsiales: Rickettsiaceae) mediated effects on the fitness and performance of Aedes aegypti (Diptera:Culicidae) under variable temperatures and initial larval densities     

2.1 Abstract          

2.2 Introduction

2.3 Materials and Methods 

Table 2.1. Experimental design.   

Table 2.2. Fitness and performance metrics.            

2.4 Results             

Figure 2.1. wAlbB relative density in females.           

Figure 2.2. wAlbB relative density in egg batches laid by experimental females.         

Figure 2.3. Fecundity and fertility results.       

Figure 2.4. Teneral dry biomass of mosquitoes.      

Table 2.3. Temperature and initial larvae density effects on adult female survival.   

Table 2.4. Temperature and initial larvae density effects on adult male survival.        

2.5 Discussion   

2.6 Conclusions

2.7 Supplementary Information   

2.8 Supplementary Tables  

Supp. Table 2.1. Temperature and initial larvae density effects on post-emergence wAlbB relative density in adult females.         

Supp. Table 2.2. Temperature and initial larvae density effects on wAlbB relative density in eggs laid by experimental females.  

Supp. Table 2.3. Temperature, initial larvae density and mosquito line effects on female fecundity.  

Supp. Table 2.4. Effects of initial larvae density and mosquito line on fertility.

Supp. Table 2.5. Initial larvae density and mosquito line effects on dry teneral female body mass.    

Supp. Table 2.6. Initial larvae density and mosquito line effects on dry teneral male body mass.         

Supp. Table 2.7. Temperature, initial larvae density and mosquito line effects on time to pupation in days.           

Supp. Table 2.8. Initial larvae density and mosquito line effects on the proportion of pupae to emerge.      

Supp. Table 2.9. Initial larvae density and mosquito line effects on the adult female proportion.         

2.9 Supplementary Figures

Supp. Figure 2.1. Adult female survival. Kaplan-Meier curves for single factors.         

Supp. Figure 2.2. Adult male survival. Kaplan-Meier curves for single factors.

Supp. Figure 2.3. Line graph of mean pupae counts/treatment/mosquito line/day.  

Supp. Figure 2.4. Emerging proportion of pupae (adults/pupae/bucket).

Supp. Figure 2.5. Setpoint temperature values for the fluctuating temperature regime.     

Chapter 3. Population dynamics of Aedes aegypti and stability of their Wolbachia infection under semi-natural intradomicile conditions            

3.1 Abstract          

3.2 Introduction

3.3 Methods         

Figure 3.1. Experimental houses in Merida (Yucatan, Mexico).           

3.4 Results             

Figure 3.2. Mosquito uninfected MID and wAlbB-carrying wMID lines, Log10 transformed counts of life stages and environmental covariates vs time.      

Figure 3.3. Fitted generalized models for the abundances of different mosquito life stages over time.          

Figure 3.4. PCR results for the proportion of A. aegypti infected with the wAlbB strain in laboratory controls and experimental populations.             

Figure 3.5. Relative quantification of wAlbB measured in Log10Ct.

3.5 Discussion   

3.6 Conclusions

3.7 Supplementary figures 

Supp. Figure 3.1. Map of the location of the experimental houses in Merida (Yucatan, Mexico).            

Supp. Figure 3.2. wAlbB effect plot of on the abundances of different immature life stages in experimental populations.    

Supp. Figure 3.3. wAlbB effect plot of on the abundances of adult forms in experimental populations.       

3.8 Supplementary tables   

Supp. Table 3.1. wAlbB effect on immature form abundances over time.             

Supp. Table 3.2. wAlbB effect on adult form abundances over time.          

Supp. Table 3.3. Results of Fisher exact test for frequency of wAlbB positive adult individuals, initial density treatment levels VS laboratory controls.    

Supp. Table 3.4. Results of Fisher exact test for frequency of wAlbB positive adult individuals, comparison between initial density treatment levels.            

Supp. Table 3.5. Results of GLM for wAlbB relative quantification in females measured as Log10Ct, comparison with laboratory controls.             

Supp. Table 3.6. Results of GLM for wAlbB relative quantification females measured as Log10Ct, effect of high initial population density.             

Supp. Table 3.7. Results of GLM for wAlbB relative quantification in males measured as Log10Ct, comparison with laboratory controls.             

Supp. Table 3.8. Results of GLM for wAlbB relative quantification males measured as Log10Ct, effect of high initial population density.             

Chapter 4. Modelling the potential influence of Wolbachia-mediated density-dependent demographic traits and loss of maternal transmission of the wAlbB strain on its introgression into Aedes aegypti populations          

4.1 Abstract          

4.2 Introduction

4.3 Methods         

Figure 4.1. Conceptualized model proposed by Hancock et. al. 2016 for the density-dependent demographic traits of the wMel strain of Wolbachia.            

Table 4.1. Model parameters: definitions and values.     

4.4 Results             

Figure 4.2. Adult abundances and Wolbachia frequencies in adults, multiple wMel and wAlbB releases.  

Table 4.2. Summary of results for multiple releases of Wolbachia: wMel and wAlbB.           

Figure 4.3. Adult abundances and Wolbachia frequencies in adults, single wMel and wAlbB releases.        

Table 4.3. Summary of results for single releases of Wolbachia: wMel and wAlbB.   

Figure 4.4. Behavior of the function driving density-dependent mean larval development times in response to values of the Beta parameter.             

Figure 4.5. Invasion dynamics of Wolbachia strains in response to single pulse releases at different release ratios.   

Table 4.4. Summary of the invasion dynamic milestones of Wolbachia strains in response to single pulse releases at different release ratios.           

Figure 4.6. Invasion dynamics of Wolbachia strains in response to combinations of release frequencies (consecutive weekly releases) at different release ratios.          

Figure 4.7. Visualization of fitted GAMs: probability of fixation in response to release frequency and release ratio.       

Figure 4.9. Visualization of fitted GAMs: Wolbachia frequency 90 days after last release in response to release frequency and release ratio.             

4.5 Discussion   

4.6 Conclusions

4.7 Supporting tables

Supp. Table 4.1. Mean development times of larvae in fluctuating temperature treatment (27-40C) and initial larvae density treatments (low: 50 larvae/liter, high: 500 larvae/liter).  

Chapter 5. General Discussion    

5.1 Summarized Findings    

5.2     Strengths and Limitations   

5.3 Future Directions 

5.4 Conclusions

References            

About this Dissertation

Rights statement
  • Permission granted by the author to include this thesis or dissertation in this repository. All rights reserved by the author. Please contact the author for information regarding the reproduction and use of this thesis or dissertation.
School
Department
Subfield / Discipline
Degree
Submission
Language
  • English
Research Field
Keyword
Committee Chair / Thesis Advisor
Committee Members
Last modified Preview image embargoed

Primary PDF

Supplemental Files