A research submitted to the Faculty of Science, University of the Witwatersrand,
Johannesburg,in partial fulfilment of the requirements for the degree of Master of Science in Environmental Science, 2018The effects of low temperatures on the metabolic rates of Anopheles quadriannulatus were
investigated by measuring the rate of carbon dioxide emission (VCO2) at different temperatures
using a closed respirometry system. In general, the metabolic rates of A. quardiannulatus
decreased with decreasing ambient temperatures. However, the decreases were not uniform over
the temperature range of 30 °C and 10 °C. Mean VCO2 measured at 30 °C and sometimes at 25
°C, were statistically different from those measured at other temperatures. Surprisingly, at 15 °C
and 10 °C, the mean VCO2 were statistically similar. It was found that metabolic rates of the
mosquitoes were affected differently if a 5 °C reduction in temperature occurred at 30 °C and when
it occurred at 15 °C. Thus, a 5 °C drop in temperature at 30 °C and 15 °C did not yield similar
percentage decrease in metabolic rates. Age was found not to impact on the metabolism of
mosquitoes except at 10 °C and 15 °C in blood fed mosquitoes (both mated and unmated). Lack
of a correlation between age and metabolic rates in these mosquitoes was a result of constant body
masses as mosquitoes aged. Mean VCO2 of four days old mosquitoes in different mating and
feeding states were found to be significantly differently only at 10 °C. Mated and blood fed
mosquitoes from this age group retained constant metabolic rates despite changes in temperature.
The finding that A. quadriannulatus is not capable of significantly dropping its metabolic rates at
low temperatures (15 °C-10 °C) is an indication that the species most probably lacks a
physiological overwintering mechanism. Consequently, its survival and longevity is highly
compromised during winter. Thus, it can be concluded that if adult A. quadriannulatus can
overwinter in cooler parts of sub-Saharan regions, it does so using non-physiological mechanisms.
Otherwise, this species and related members of Anopheles gambiae overwinters in developmental stages other than adulthood. In this way, these mosquitoes are able perpetuate their populations
post winter season.XL201
