Abstract
Wolbachia infections are being introduced into mosquito vectors of human diseases following the discovery that they can block transmission of disease agents. This requires mosquitoes infected with the disease-blocking Wolbachia to successfully invade populations lacking the infection. While this process is facilitated by features of Wolbachia, particularly their ability to cause cytoplasmic incompatibility, blocking Wolbachia may produce deleterious effects, such as reduced host viability or fecundity, that inhibit successful local introductions and subsequent spatial spread. Here, we outline an approach to facilitate the introduction and spread of Wolbachia infections by coupling Wolbachia introduction to resistance to specific classes of insecticides. The approach takes advantage of very high maternal transmission fidelity of Wolbachia infections in mosquitoes, complete incompatibility between infected males and uninfected females, the widespread occurrence of insecticide resistance, and the widespread use of chemical control in disease-endemic countries. This approach is easily integrated into many existing control strategies, provides population suppression during release and might be used to introduce Wolbachia infections even with high and seasonally dependent deleterious effects, such as the wMelPop infection introduced into Aedes aegypti for dengue control. However, possible benefits will need to be weighed against concerns associated with the introduction of resistance alleles.
Highlights
There is increasing interest in using Wolbachia bacterial infections to suppress mosquito-transmitted diseases. This follows the successful introduction of Wolbachia into disease vectors, Aedes aegypti Linnaeus, 1762 [1] and Aedes albopictus Skuse, 1894 [2], and the realization that Wolbachia act as natural agents to suppress disease [3,4]
Inherited Wolbachia possess several characteristics that facilitate their invasion and rapid spread into natural populations [7], their ability to cause cytoplasmic incompatibility that leads to embryo death when uninfected females mate with infected males
To explore potential effects of coupling resistance alleles to Wolbachia introductions on unstable points, we present idealized analyses aimed at approximating the quantitative effects rather than capturing specific biological details
Summary
There is increasing interest in using Wolbachia bacterial infections to suppress mosquito-transmitted diseases. The wMelPop infection provides complete blockage of dengue [5], but A. aegypti mosquitoes with this infection suffer significantly reduced fecundity and egg hatch, when eggs are in a dry quiescent state [10,11] This feature makes it more difficult to introduce wMelPop into populations as reflected by its rate of increase in semi-natural population cages when compared with wMel [1]. Once introduced into a local area, the infection may be lost following mosquito migration from surrounding uninfected populations [9] or during the dry season when wMelPop imposes a substantial fitness cost [10] To counter these issues, a method is needed to facilitate the spread of Wolbachia that is consistent with current control methods and acceptable in countries where diseases are endemic. The strategy could help secure the persistence of infections such as wMelPop across a dry season and assist their spatial spread, as long as the unstable equilibrium (the frequency of Wolbachia in a population that needs to be exceeded for the Wolbachia to spread to fixation) is not prohibitively high [9]
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