  The assumption that vector mortality remains constant with age is used widely
to assess malaria transmission risk and predict the public health consequences
of vector control strategies. However, laboratory studies commonly demonstrate
clear evidence of senescence, or a decrease in physiological function and
increase in vector mortality rate with age. We developed methods to integrate
available field data to understand mortality in wild Anopheles gambiae, the
most import vector of malaria in sub-Saharan Africa. We found evidence for an
increase in rates of mortality with age, a component of senescence. As
expected, we also found that overall mortality is far greater in wild cohorts
than commonly observed under protected laboratory conditions. The magnitude of
senescence increases with An. gambiae lifespan, implying that wild mosquitoes
die long before cohorts can exhibit strong senescence. We reviewed available
published mortality studies of Anopheles spp. to confirm this fundamental
prediction of aging in wild populations. Senescence becomes most apparent in
long-living mosquito cohorts, and cohorts with low extrinsic mortality, such as
those raised under protected laboratory conditions, suffer a relatively high
proportion of senescent deaths. Imprecision in estimates of vector mortality
and changes in mortality with age will severely bias models of vector borne
disease transmission risk, such as malaria, and the sensitivity of transmission
to bias increases as the extrinsic incubation period of the parasite decreases.
While we focus here on malaria, we caution that future models for
anti-vectorial interventions must therefore incorporate both realistic
mortality rates and age-dependent changes in vector mortality.
