Susceptibility of Anopheles mosquito to agricultural insecticides in the Adansi North district, Ghana

This study determined the susceptibility of Anopheles mosquitoes to some agricultural insecticides used in the Adansi North District of the Ashanti Region, and the efficacy of Actellic (pirimiphos-methyl) 50 EC as an alternative insecticide for the control of mosquitoes in the district. Anopheles larvae were collected from mosquito breeding sites near farms. Five insecticides were assayed, pirimiphos-methyl (0.9%), DDT (4%), propoxur (0.1%), deltamethrin (0.05%), and lambda-cyhalothrin (0.05%). The residual efficacy of pirimiphos-methyl 50 EC sprayed on two surfaces (mud and cement) were determined by cone bioassay test at two-weekly intervals for 15 weeks after spraying. The susceptibility test showed the levels of phenotypic resistance of Anopheles spp. to the agricultural insecticides. Anopheles gambiae s.l. (96.50%) was the most dominant Anopheles species. The principal malaria vector in the district was resistant to DDT, Propoxur, Deltamethrin, and Lambda-cyhalothrin. Pirimiphos-methyl an organophosphate remained effective against the malaria vector. Student t-test analysis of bioassay test results showed that statistically the average mortality of Anopheles mosquitoes on cement surface was higher than the average mortality on mud surface. In conclusion, agricultural insecticides used in the district were negatively affecting malaria vector control activities. The use of pirimiphos-methyl (Actellic 50 EC) as an alternative insecticide against the malaria vector was more effective on cemented wall surface than on mud surface wall.