POTENTIAL METHODS OF TARGETING LARVAL SOURCE MANAGEMENT USING ANOPHELES HABITAT DISTRIBUTION AND PRODUCTIVITY OF ADULT MOSQUITOES IN THREE HIGHLAND VALLEYS

Larval Source Management (LSM) has had enormous historical successes that clearly indicate that it can play an important role in reducing malaria transmission. This is due to the increasing challenge of resistance development by malaria parasites to drugs and malaria vectors to insecticides. Recent renewed interest in larval control is advocating for targeted malaria vector control in their aquatic stages with an aim of making it less labour intensive. The objective of this study was to evaluate potential methods of targeting LSM against malaria vectors using Anopheles habitat distribution and productivity of adult mosquitoes. This study was done in three selected basin-like valleys of Musilongo, Emutete and Kezege within the western Kenya highlands. The presence of anopheline larvae in habitats was determined using dipping method twice per month at an interval of two weeks. The collected data was analyzed using an indicator of local clustering that measures the „concentration‟ of spatially distributed attribute variable, the Gi*(d) local statistic, in order to identify spatial and temporal distribution patterns in the presence of anopheline larvae in habitats. Abundance of aquatic macro-organisms and the productivity of adult mosquitoes, specifically malaria vectors, were sampled using a sweep-net from: (1) nine habitats selected from each of the natural swamps, cultivated swamps, river fringes, puddles, open drains and burrow pits; (2) eighteen habitats each selected from the habitats more and less frequently found with anopheline larvae, and (3) from twenty experimental pools that were created at Emutete. Generalized Estimating Equations (GEE) were used to identify factors that significantly determined the presence and abundance of aquatic organisms and the productivity of adult Anopheles mosquitoes from these habitats. The Gi*(d) statistic identified spatial and temporal clusters of anopheline presence in habitats within the three valleys, which were different among the valleys and the rainfall seasons. Although the productivity of Anopheles gambiae sensu lato was higher in puddles than in the other five habitat types, this habitat type was the least stable, smallest in surface extension and formed 5.4% of all habitats. The productivity of An. gambiae s.l. adults was significantly higher in the habitats more frequently found with anopheline larvae than the less frequent ones. However, habitats more frequently found with anopheline larvae formed 5.6% of all habitats. The productivity of Culex mosquitoes in experimental pools that were created was highest during the dry season whereas that of An. gambiae s.l. was significantly high during the rainy season. The findings of this study highlight the possibilities of targeting LSM against An. gambiae s.l. mosquitoes using maps generated from the Gi*(d) local statistic and in time during the main rainy season. However, there was no such possibility to use different habitat types and occurrences of anopheline larvae in habitats as determining factors to target LSM against An. gambiae s.l. mosquitoes.