The use of sequential mark-release-recapture experiments to estimate population size, survival and dispersal of male mosquitoes of the Anopheles gambiae complex in Bana, a west African humid savannah village.

BACKGROUND: Vector control is a major component of the malaria control strategy. The increasing spread of insecticide resistance has encouraged the development of new tools such as genetic control which use releases of modified male mosquitoes. The use of male mosquitoes as part of a control strategy requires an improved understanding of male mosquito biology, including the factors influencing their survival and dispersal, as well as the ability to accurately estimate the size of a target mosquito population. This study was designed to determine the seasonal variation in population size via repeated mark-release-recapture experiments and to estimate the survival and dispersal of male mosquitoes of the Anopheles gambiae complex in a small west African village.

METHODS: Mark-release-recapture experiments were carried out in Bana Village over two consecutive years, during the wet and the dry seasons. For each experiment, around 5000 (3407-5273) adult male Anopheles coluzzii mosquitoes were marked using three different colour dye powders (red, blue and green) and released in three different locations in the village (centre, edge and outside). Mosquitoes were recaptured at sites spread over the village for seven consecutive days following the releases. Three different capture methods were used: clay pots, pyrethroid spray catches and swarm sampling.

RESULTS: Swarm sampling was the most productive method for recapturing male mosquitoes in the field. Population size and survival were estimated by Bayesian analyses of the Fisher-Ford model, revealing an about 10-fold increase in population size estimates between the end of dry season (10,000-50,000) to the wet season (100,000-500,000). There were no detectable seasonal effects on mosquito survival, suggesting that factors other than weather may play an important role. Mosquito dispersal ranged from 40 to 549 m over the seven days of each study and was not influenced by the season, but mainly by the release location, which explained more than 44% of the variance in net dispersal distance.

CONCLUSION: This study clearly shows that male-based MRR experiments can be used to estimate some parameters of wild male populations such as population size, survival, and dispersal and to estimate the spatial patterns of movement in a given locality.