Estimation of survival rates in haematophagous insects

Estimation of the survival rate through a gonotrophic cycle is an important factor in determining the vectorial capacity of a population of haematophagous insects in a disease cycle. Most methods used to calculate survival rates make stringent assumptions which may not be valid for all species. Birley and colleagues used a time series analysis of samples collected over several consecutive days, the lagged parous rate. Here, we use a simulation model to investigate (i) the length of data series needed and (ii) the consequences of failures in the assumptions of this method for the estimated survival rate. The accuracy of the estimated survival rate per cycle was high with sample periods of 10-100 days. The standard deviation (a measure of precision) decreased with the length of the sample period. When random sampling efficiency was included, the accuracy remained high but the estimates were less precise (larger standard deviations). If the sampling was biased in favour of either nulliparous or parous females, estimates of the survival rate were not accurate. The relationship between estimated survival rate, bias in collection, and true survival rate was non-linear. Thus, correction for the bias requires (i) prior knowledge of the direction and the severity of the bias and (ii) an independent estimate of the survival rate. This method of estimating survival rates is less accurate when the collection method is biased for or against parous females, although robust to other assumptions.