5.3 Controlling mosquito populations and disease transmission
There have been several mechanistic modelling efforts to understand how regional and seasonal environmental variation will impact the relative reproductive number of a pathogen, the intensity of human transmission, and the efficacy of key disease interventions (e.g., Zika; Ngonghalaet al. (2021), schistosomiasis; Nguyen et al. (2021)). These studies have, again, focused largely on the effects of ambient temperature. However, seasonal and regional variation in humidity and precipitation could extend or shorten the transmission season and magnify or depress the intensity of epidemics as predicted from models incorporating the effects of temperature alone (Huber et al.2018; Ngonghala et al. 2021). For example, this is likely to be the case in seasonally dry environments where mosquito-borne disease transmission tends to be highest during or just after the rainy season and lowest during the hottest / driest parts of the season due to seasonal shifts in mosquito habitat, as well as the effects of temperature and humidity on mosquito and pathogen traits relevant for transmission.
How variation in humidity affects the efficacy of current and novel mosquito control interventions also needs to be considered. Many novel mosquito control technologies involve the mass release of males that have been sterilized or genetically engineered to pass on traits that confer either severe fitness costs (i.e., population suppression approaches; Alphey et al. 2010; Wilke & Marrelli 2012; Wanget al. 2021) or enhanced resistance to human pathogens (i.e., population replacement approaches (Wilke & Marrelli 2015; Carballar-LejarazĂș & James 2017; Hegde & Hughes 2017)). For example, the w Mel strain of the symbiont Wolbachia can prevent dengue, chikungunya, and Zika transmission in Ae. aegypti(Moreira et al. 2009; Ye et al. 2015; Aliota et al.2016a, b). Experimental work has determined that w Mel infections are temperature sensitive, with high temperatures causing reductions inWolbachia density (Ulrich et al. 2016; Ross et al.2017, 2019, 2020; Foo et al. 2019; Gu et al. 2022) and temperature variation affects the host-pathogen interaction and the outcome of infection in Wolbachia -infected mosquitoes (Murdocket al. 2014a). Based on the relationship between temperature and water balance laid out in this paper, further experiments should examine whether Wolbachia infections are limited by temperature alone or by cellular water availability, and examine what role mosquito desiccation stress plays in limiting Wolbachia abundance within mosquitoes at varying temperature.
Furthermore, thermal performance differs between insecticide resistant vectors and their susceptible counterparts, with important implications for assessing fitness costs associated with insecticide resistance (Akinwande et al. 2021). Thus, insecticide resistant mosquitoes may have to optimize temperature and water needs across environmental constraints differently, and therefore be affected by changes in humidity, with potentially important consequences for population dynamics, mosquito-pathogen interactions, and transmission. Identifying these environmental constraints on efficacy and coverage will be critical for the successful implementation of current and future control programs (Parham & Hughes 2015).