The influence of feeding behaviour and temperature on the capacity of mosquitoes to transmit malaria

Insecticide-treated bed nets reduce malaria transmission by limiting
contact between mosquito vectors and human hosts when mosquitoes feed
during the night. However, malaria vectors can also feed in the early
evening and in the morning when people are not protected. Here, we
explored how timing of blood feeding interacts with environmental
temperature to influence the capacity of Anopheles mosquitoes to transmit
the human malaria parasite, Plasmodium falciparum. In laboratory
experiments, we found no effect of biting time itself on the proportion of
mosquitoes that became infectious (vector competence) at constant
temperature. However, when mosquitoes were maintained under more realistic
fluctuating temperatures there was a significant increase in competence
for mosquitoes feeding in the evening (18:00h), and a significant
reduction in competence for those feeding in the morning (06:00h),
relative to those feeding at midnight (00:00h). These effects appear to be
due to thermal sensitivity of malaria parasites during the initial stages
of parasite development within the mosquito, and the fact that mosquitoes
feeding in the evening experience cooling temperatures during the night,
whereas mosquitoes feeding in the morning quickly experience warming
temperatures that are inhibitory to parasite establishment. A transmission
dynamics model illustrates that such differences in competence could have
important implications for malaria prevalence, the extent of transmission
that persists in the presence of bed nets, and the epidemiological impact
of behavioural resistance.  These results indicate the
interaction of temperature and feeding behaviour could be a major
ecological determinant of the vectorial capacity of malaria mosquitoes.