Effective residual life of bendiocarb insecticide on sprayed surfaces

Effective residual life of insecticides on sprayed surfaces determines the number of spraying cycles required to cover malaria transmission season. However, residual efficacy of insecticides varies with spray surface type. This study assessed effective residual life of bendiocarb on cow dung plastered and mud plastered wall surface types of human dwellings against An. arabiensis.  Wall cone bioassays were carried out following the WHO (World Health Organization) standard operating procedures. Percentage mortality was calculated according to WHO bioassay protocol and Poisson regression model was fitted to show the association of mosquito mortality with explanatory variables using SAS (SAS Institute Inc. 2016. SAS® 9.4 Language Reference: Concepts, Sixth Edition. Cary, NC: SAS Institute Inc.). Efficacy of bendiocarb against An. arabiensis was 100% for the first 35 days on both cow dung and mud wall surface types. However, its efficacy deteriorated earlier on non-plastered wall surfaces after 35 days. The relationship between mosquito mortality and explanatory variables was: Mortality =3.637542, Sprayed = + 0.282841, Plastering= - 0.0094612 35-Days after spray, - 0.600159 65-Days after spray. Because coefficients for cone position were not significant, they were excluded from the regression equation. Generally, the effective residual life of bendiocarb on mud plastered wall surface was too short to cover malaria transmission season. Therefore, alternative insecticide with longer residual effective life is required in areas having more than two months of malaria transmission season.