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FP7

WOLBACHIA_MOD Report Summary

Project reference: 326551
Funded under: FP7-PEOPLE

Periodic Report Summary 1 - WOLBACHIA_MOD (The ecology and population dynamics of Wolbachia infections in Aedes aegypti and the development of new strategies for mosquito-borne disease control)

The ecology and population dynamics of Wolbachia infections in Aedes aegypti and the development of new strategies for mosquito-borne disease control

Project website: http://zoo-godfray.zoo.ox.ac.uk/people/dr-penelope-hancock/

Project objectives:
(i) To empirically examine the dynamics of Wolbachia infections in Aedes aegypti populations under competitive conditions of limited larval food resources.
(ii) To develop data-driven mathematical models to predict strategies for field release of Wolbachia into Aedes aegypti populations that are robust to endogenous and exogenous environmental variation.

Research activities performed during the period:
(i) Empirical research: We performed three empirical studies that observed Wolbachia invasion dynamics in Aedes aegypti mosquito populations, each housed in a semi-field cage. The developing mosquito larvae were supplied with regular, fixed amounts of food in order to simulate conditions of larval food limitation. Each population was maintained for a period of approximately 6 months, and we monitored the abundance of the juvenile mosquito life stages over time. In two populations, we introduced Wolbachia and monitored its infection frequency over time. In one of these populations we also monitored adult wing length (as a proxy for body size). The third population did not contain Wolbachia, and experienced a lower larval food supply. Study of the third population aims to assess effects of variation in the larval food supply on mosquito population dynamics.
(ii) Mathematical modelling research: We have developed two kinds of mathematical models to analyse the results of our empirical studies:
1. We developed a Bayesian statistical methodology to infer the development times of each cohort of larvae in our mosquito population time series. This involved inference of the full development time distributions of the larval cohorts. We also developed quantitative methods for estimating the average adult female fecundity over time.
2. We developed a predictive demographic model of mosquito-Wolbachia dynamics that incorporates larval density-dependent variation in three vital mosquito fitness components: average adult female fecundity and larval development time and survival. Sub-models models of density-dependent mosquito demographic rates were inferred using Bayesian statistical methods informed by data from our semi-field cage population studies. Separate estimates of demographic rates were obtained for the infected and uninfected subpopulations.

Main results achieved thus far
1. Our Bayesian statistical methodology provides an accurate fit to the observed mosquito abundances and yields estimates of three vital mosquito fitness components over time (average female fecundity and larval development time and survival). All three demographic rates were strongly associated with variation in larval density. Thus our study provides the first quantification of density-dependent regulation in an A. aegypti population under food-limited conditions in terms of these fitness components.
2. Using our estimated mosquito demographic rates we have assessed differences between larval demographic rates of infected and uninfected mosquitoes under intrinsic population dynamics. We applied this methodology to the first semi-field cage population and found that accurate predictions of Wolbachia frequency dynamics were obtained by assuming no difference in larval demographics.
3. Our mathematical model of density-dependent mosquito-Wolbachia dynamics accurately predicts the observed dynamics in our semi-field cage populations. This methodology provides estimates of differences in mosquito fitness components between infected and uninfected phenotypes. We found no significant difference in predicted average female fecundity, but in the second population infected larvae were superior competitors.
4. We compare our model predictions to those obtained by widely-used models of Wolbachia dynamics that ignore density-dependent variation in host fitness. We find that our model predicts a comparatively slow rate of Wolbachia invasion (Figure 1). This demonstrates that larval density-dependent variation in mosquito fitness has an important effect on Wolbachia invasion and needs to be considered in predicting the dynamics associated with field release of Wolbachia.

Expected final results and potential impact and use
We will provide a new transferrable computational methodology for predicting Wolbachia invasion in A. aegypti that incorporates effects of density-dependent fitness heterogeneity in the mosquito population. Using this model we will develop guidelines for the design of field release strategies aimed at achieving rapid and effective Wolbachia invasion. Current field release trials aim to establish Wolbachia in areas of south-east Asia and South America, within geographic regions that bear the highest dengue burden. Our results will enhance the capacity to understand and interpret the results of these field trials and to design release strategies that increase the potential of Wolbachia to control dengue.

Related information

Contact

Wells, Gill (Head of European Team)
Tel.: +44 1865 289800
Fax: +44 1865 289800
E-mail

Subjects

Life Sciences
Record Number: 184168 / Last updated on: 2016-06-08
Information source: SESAM