High temperature cycles result in maternal transmission and dengue infection differences between Wolbachia strains in Aedes aegypti

Abstract

Environmental factors play a crucial role in the population dynamics of arthropod endosymbionts, and therefore in the deployment of Wolbachia symbionts for the control of dengue arboviruses. The potential of Wolbachia to invade, persist and block virus transmission depends in part on its intracellular density. Several recent studies have highlighted the importance of larval rearing temperature in modulating Wolbachia densities in adults, suggesting that elevated temperatures can severely impact some strains, while having little effect on others. The effect of a replicated tropical heat cycle on Wolbachia density and levels of virus blocking was assessed using Aedes aegypti lines carrying strains wMel and wAlbB, two Wolbachia strains currently used for dengue control. Impacts on intracellular density, maternal transmission fidelity and dengue inhibition capacity were observed for wMel. In contrast wAlbB-carrying Ae. aegypti maintained a relatively constant intracellular density at high temperatures and conserved its capacity to inhibit dengue. Following larval heat treatment, wMel showed a degree of density recovery in aging adults, although this was compromised by elevated air temperatures. When choosing the Wolbachia strain to be used in a dengue control programme it is important to consider the effects of environmental temperatures on invasiveness and virus inhibition. Author summaryIn the past decades, dengue incidence has dramatically increased all over the world. An emerging dengue control strategy utilizes Ae. aegypti mosquitoes artificially transinfected with the bacterial symbiont Wolbachia, with the ultimate aim of replacing wild mosquito populations. Wolbachia is transmitted from mother to offspring and is able to interfere with virus transmission within the mosquito vector. However, the rearing temperature of mosquito larvae is known to impact on some Wolbachia strains. In this study, we compared the effects of a temperature cycle mimicking natural breeding sites in tropical climates on two Wolbachia strains, currently used for open field trials. We observed that the strain wMel was susceptible to high larval rearing temperatures, while the strain wAlbB resulted to be more stable. These results underlines the importance of understanding the impact of environmental factors on released mosquitoes, in order to ensure the most efficient strategy for dengue control.