Metabolic rate does not vary with seasonal change in Anopheles arabiensis adults in South Africa.

ABSTRACT

An important component of South Africa's malaria elimination agenda is identifying the entomological drivers of residual transmission, especially those that present opportunities for enhanced vector control. Seasonal mosquito density correlates directly with malaria transmission in South Africa. Transmission is highest during the warm rainy season and lowest but not entirely absent during the cooler dry season. The factors that sustain dry-season mosquito survival remain unknown. The aim of this project was therefore to investigate seasonal change in metabolic rate to determine the presence or absence of winter dormancy in malaria vector mosquitoes. Metabolic rate, determined by CO2 production during closed-system respirometry, was measured from wild anophelines collected from KwaZulu-Natal Province, South Africa. Monthly sampling spanned all four seasons (summer, autumn, winter, and spring) in 2017. Anopheles arabiensis and An. parensis specimens formed the majority of the total 437 identified specimens (n = 216 and n = 162, respectively). Metabolic rate data from wild-caught mosquitoes showed no significant seasonal disparities for An. arabiensis and An. parensis males and females. Further laboratory experiments assessed the effect of manipulated photoperiod, representing seasonal day-length changes, on the metabolic rate of colonized An. arabiensis mosquitoes. Simulations of midwinter (10 h14 h light dark) and midsummer (14 h10 h) day-length showed no significant effect on the metabolic rate of these mosquitoes. Age (in days) had a significant effect on the metabolic rate of both male and female colonized adult An. arabiensis mosquitoes which may be linked to developmental factors during maturation of adults. These data suggest that the South African populations of the malaria vector species An. arabiensis and An. parensis do not curtail their breeding and foraging activities during the colder and drier winter months. Overwintering by diapause does not appear to be triggered in the adult mosquito stage in An. arabiensis. However, their respective population densities do decrease considerably during winter leading to reduced malaria transmission and the opportunity for control by winter larviciding of known breeding sites.