Investigation of cuticular hydrocarbons for determining the age and survivorship of Australasian mosquitoes

The cuticular hydrocarbon (CH) technique of age grading mosquitoes was evaluated for use on laboratory-reared Aedes aegypti (L.), Anopheles farauti (Laveran), and Ochlerotatus vigilax (Skuse). Gas chromatography/mass spectroscopy was used to determine the relative abundance of five alkanes in hexane extracts from the legs of individual mosquitoes. Age-related changes to relative hydrocarbon abundances were observed from An. farauti and Ae. aegypti, which are vectors of malaria and dengue, respectively. Female An. farauti were classified into two age categories (1-5 and ! 5 days old at 27 degrees C) and Ae. aegypti into three age categories (1 to < 5, 5 to < 9 and >= 9 days old at 27 degrees C) based on these changes. However, there was an absence of predicable age-related changes to hydrocarbon abundance in Oc. vigilax. Simulation modeling was used to construct sequential sampling guidelines for the application of this technique to estimate the survivorship of Ae. aegypti and An. farauti populations. These guidelines define the relationship between the survival rate, number of mosquitoes sampled, CH-based predictions of age, and the accuracy of survival rate estimates. They demonstrated, for example, that if 19% of a population of Ae. aegypti is estimated to be >= 9 days old by CH analysis, an estimate of the daily survival rate from the exponential model should be based on a sample of 200 mosquitoes for the survival rate estimate to be within 5% of the actual rate. However, if only 10% of the population is estimated to be >= 9 days old, 500 mosquitoes would need to be analyzed for the survival rate estimate to be of equivalent accuracy.