Estimating age structure of wild Anopheles populations using the captive cohort method

The captive cohort method is a simple and inexpensive way to estimate age structure of wild populations of insects. This method is based on the concept that post-capture survival is linked with age at capture and that a population’s age structure can be estimated from its death distribution. The main purpose of this study is to adapt and optimize protocols for the captive cohort method for use with Anopheles mosquitoes. Following studies using lab-reared female Anopheles stephensi, female Anopheles freeborni were live-trapped from field sites in Butte County and Sutter County, California, and individually survived forward in modified polystyrene cuvettes and polypropylene conical tubes under constant lab conditions to observe behavior and record time until death. Post-capture survival for each mosquito was used to estimate patterns in population age structure and minimum and maximum longevity of the sampled population over the Aug-Sept collection period. This protocol can be used as a low-tech tool to collect data for daily survival probability in real-time for more accurate estimates of vectorial capacity.