Dyeing process may alter the efficacy of insecticide-treated nets

The biological efficacy as judged by mortality against Anopheles gambiae s.s. of three net samples, one white and two colored, treated with deltamethrin by conventional dipping was compared. Efficacy as well as chemical analysis results showed that uptake of insecticide by white net material was much higher than by colored nets. After a single wash, efficacy of colored nets was reduced significantly below 80% mortality, which is the minimum acceptable level for a field application. This unexpected result could be because of either low uptake of insecticide by colored fibers or high alkalinity on the fibers, resulting from the dyeing process (reduction clearing). alpha-Cyanopyrethroids, such as deltamethrin, have a low stability in alkaline conditions and rapidly degrade. Practical implications of this finding are of primary importance because the majority of nets currently purchased by institutional buyers for malaria prevention are colored.