Heatwaves cause fluctuations in wMel Wolbachia densities and frequencies in Aedes aegypti

Abstract

Aedes aegypti mosquitoes infected with the wMel strain of Wolbachia are being released into natural mosquito populations in the tropics as a way of reducing dengue transmission. High temperatures adversely affect wMel, reducing Wolbachia density and cytoplasmic incompatibility in some larval habitats that experience large temperature fluctuations. We monitored the impact of a 43.6˚C heatwave on the wMel infection in a natural population in Cairns, Australia, where wMel was first released in 2011 and has persisted at a high frequency. Wolbachia infection frequencies in the month following the heatwave were reduced to 83% in larvae sampled directly from field habitats and 88% in eggs collected from ovitraps, but recovered to be near 100% four months later. Effects of the heatwave on wMel appeared to be stage-specific and delayed, with reduced frequencies and densities in fieldcollected larvae and adults reared from ovitraps but higher frequencies in field-collected adults. Laboratory experiments showed that the effects of heatwaves on cytoplasmic incompatibility and density are life stage-specific, with first instar larvae being the most vulnerable to temperature effects. Our results indicate that heatwaves in wMel-infected populations will have only temporary effects on Wolbachia frequencies and density once the infection has established in the population. Our results are relevant to ongoing releases of wMel-infected Ae. aegypti in several tropical countries.

Reduced dengue incidence following deployments of Wolbachia-infected Aedes aegypti in Yogyakarta, Indonesia: a quasi-experimental trial using controlled interrupted time series analysis

“…However we found no evidence that wMel establishment was compromised in the climatic conditions of Yogyakarta. Elsewhere Ross et al reported that heatwaves have only transient effects on wMel frequencies in Australia 29 . Evidence from pilot field studies is likely the best method for selecting the optimal Wolbachia strain for deployment in a given setting.…”

Reduced dengue incidence following deployments of Wolbachia-infected Aedes aegypti in Yogyakarta, Indonesia: a quasi-experimental trial using controlled interrupted time series analysis

“…However we found no evidence that wMel establishment was compromised in the climatic conditions of Yogyakarta. Elsewhere Ross et al reported that heatwaves have only transient effects on wMel frequencies in Australia[29]. Evidence from pilot field studies is likely the best method for selecting the optimal Wolbachia strain for deployment in a given setting.By chance, the commencement of Wolbachia releases in the quasi-experimental study area in late 2016 coincided with the largest dengue epidemic on record in Yogyakarta City.Unsurprisingly, dengue case notifications to the District Health Office from across Yogyakarta City were then lower during 2017 and 2018 than in any two-year period in the previous 25 years, and it is notable that a highly significant Wolbachia-associated effect was observed even during this period of record low dengue transmission.…”

Modeling the potential of wAu-Wolbachia strain invasion in mosquitoes to control Aedes-borne arboviral infections

“…Other features of Wolbachia which serve as liabilities in mosquitoes include: imperfect maternal transmission (IMT) 30,37 and loss of Wolbachia infection (LWI). LWI impedes the establishment of Wolbachia-infected mosquitoes and is a result of mosquito vulnerability to high temperature 38,39 .…”