Insecticide resistance testing in malaria vectors in Tanzania: Challenges in mosquito sampling and rearing under field conditions

Abstract

Background: The National Institute for Medical Research, Amani centre, in collaboration with National Malaria Control Programme, has been conducting annual insecticide resistance surveillance since 1999, aimed at early detection of resistance to insecticides used for malaria control in Tanzania. The Standard WHO method for larvae collection and rearing were used but challenges and limitations were  encountered. For example rearing the larvae and adult mosquitoes using the Standard WHO method experienced 100% mortality for larvae; and adults in three days. The researchers therefore made modifications to the Standard WHO  method to create suitable tools for the   field environment. Methods: A ladle was created from an empty water bottle in which an oval hole   longitudinally  cut  halfway from the bottom. Instead of using TetraMin as mosquito larval food, green algae were collected from mosquito breeding sites and used as larval food.  Improvised heater of charcoal stoves and humidifier of wet fabric such as “Kanga” and “Kitenge” were also used. Results and conclusion: There was 90% larval  survival, adult mosquito survived much better and the scientists had a total of 467 mosquitoes to run the insecticide susceptibility tests. Innovative ways are  necessary under field conditions for mosquito breeding in susceptibility studies.

Key words: Malaria, Anopheles gambiae complex, larvae, fabric, resistance, susceptibility, Tanzania.