The role of agricultural chemicals on anopheles arabiensis vector ‘fitness’ in malaria transmission in a rice agro-ecosystem i

Abstract

Control of African malaria vectors is dependent on insecticides via residual sprays IRS or insecticide treated nets ITNs. Emergent vector resistance to pyrethroids in sub-Saharan Africa and development of alternative insecticides, treatments and vaccines against malaria is expensive and long-term. New tools for vector control to achieve interruption of malaria transmission needs priority considering the long-term challenge of malaria eradication. Increased knowledge on the ecology and behavior of malaria vectors in their habitats is necessary. The effects of agro-chemicals in rice cultivation on malaria vector ‘fitness’ was investigated in Mwea irrigation scheme Kenya, for its potential application as a novel vector control strategy. During the rice-growing period of September 2010 to January 2011, four agro-chemicals were evaluated for their effects on vector ‘fitness’ in paddy and simulated field experiments. Pupas were sampled in agro-chemical exposed paddies and mosquito eggs incubated in simulated conditions of different agrochemical combinations. Emergent female Anophelines were reared until death. Longevity in days and wing length in millimeters were used as parameters for mosquito ‘fitness’. Emergent adults had a mean lifespan of 6.5 days in paddies and 7.1 days in simulated trials. Experiment control mosquitoes had a mean longevity of 18 days in the paddies and 15 days in simulated trial. The mean wing length was 3.5 mm in the agrochemical paddy-exposed vectors and 3.7 mm for the simulated experiment compared to 3.1 mm and 3.2 mm in the field control and simulated experiment respectively. Longevity was significantly affected by agrochemicals in both paddy (P = 0.003) and simulated experiment (P = 0.00). Agrochemicals used in Mwea irrigation scheme decreased mosquito longevity with minimal size encumbrance. These findings suggest that systematic use of agrochemicals in rice irrigation contribute to low malaria transmission by shortened Anopheles arabiensis life span and proper agrochemical use is a potential malaria vector control strategy. The results of this study need to be experimented in other agro-ecosystems for use as a passive malaria transmission control tool.