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).