Short persistence of bendiocarb sprayed on pervious walls and its implication for the indoor residual spray program in Ethiopia

Abstract

BackgroundWith the emergence and spread of vector resistance to pyrethroids and DDT in Africa, several countries have recently switched or are considering switching to carbamates and/or organophosphates for indoor residual spraying (IRS). However, data collected on the residual life of bendiocarb used for IRS in some areas indicate shorter than expected bio-efficacy. This study evaluated the effect of pH and wall type on the residual life of the carbamates bendiocarb and propoxur as measured by the standard World Health Organization (WHO) cone bioassay test.MethodsIn phase I of this study, bendiocarb and propoxur were mixed with buffered low pH (pH 4.3) local water and non-buffered high pH (pH 8.0) local water and sprayed on two types of wall surface, mud and dung, in experimental huts. In the six month phase II study, the two insecticides were mixed with high pH local water and sprayed on four different surfaces: painted, dung, mud and mud pre-wetted with water. The residual bio-efficacy of the insecticides was assessed monthly using standard WHO cone bioassay tests.ResultsIn phase I, bendiocarb mixed with high pH water killed more than 80 % of susceptible Anopheles arabiensis mosquitoes for two months on both dung and mud surfaces. On dung surfaces, the 80 % mortality threshold was achieved for three months when the bendiocarb was mixed with low pH water and four months when it was mixed with high pH water. Propoxur lasted longer than bendiocarb on dung surfaces, staying above the 80 % mortality threshold for four and five months when mixed with high and low pH water, respectively. Phase II results also showed that the type of surface sprayed has a significant impact on the bio-efficacy of bendiocarb. Keeping the spray water constant at the same high pH of 8.0, bendiocarb killed 100 % of exposed mosquitoes on impervious painted surfaces for the six months of the study period compared with less than one month on mud surfaces.ConclusionsMixing the insecticides in alkaline water did not reduce the residual bio-efficacy of bendiocarb. However, bendiocarb performed much better on impervious (painted) surfaces than on porous dung or mud ones. Propoxur was less affected by wall type than was bendiocarb. Studies on the interaction between wall materials, soil, humidity, temperature and pH and the residual bio-efficacy of new and existing insecticides are recommended prior to their wide use in IRS.

Evaluation of long-lasting indoor residual spraying of deltamethrin 62.5 SC-PE against malaria vectors in India

“…This might be due to the fact that the residual life of insecticides depends upon the type of surfaces [5]. The reason for faster decline of insecticides on mud surfaces as shown in the current study is due to more porous nature compared to smoother surfaces (cement and wood) and dung surfaces as observed in another study [30]. In the study villages, 100% of households were found to have re-plastered their walls by 8.5 months.…”

“…jeyporiensis (n = 120) was observed on wall surfaces in both the arms before spraying, confirming the absence of insecticide deposits on the walls. At 1,7,15,30,45,60, and 75 days post-spraying, none of the sprayed surfaces (mud, cement, wood) of both the formulations gave below 100.0% corrected mortality. One-hundred and five days after spraying, while deltamethrin 62.5 SC-PE caused mortality of 87.5, 92.5 and 90.0% in mud, cement and wood surfaces, respectively (Fig.…”

Determination of the residual efficacy of carbamate and organophosphate insecticides used for indoor residual spraying for malaria control in Ethiopia

“…For both rough and smooth mud, the mortality was below 80% after 1 month, and the mortality on rough mud did not exceed 80% immediately after spraying. While poor results of bendiocarb on these surfaces have been previously reported from Ethiopia [ 6 ], these results are of concern. However, the performance of bendiocarb on painted surfaces was considerably better, lasting longer for 4 months.…”

“…To this end, the residual efficacy of propoxur and bendiocarb were evaluated by the President’s Malaria Initiative-funded Ethiopia Africa Indoor Residual Spraying (AIRS) project [ 6 ]. The residual efficacy of the two insecticides were compared over a period of 6 months on several substrates, and it was found that bendiocarb (400 mg/m 2 ) had a short residual life on porous surfaces, whereas propoxur (2000 mg/m 2 ) resulted in over 80% mortality of mosquitoes in 30 min cone tests for at least 6 months on all surfaces tested [ 6 ].…”

Insecticide resistance in Anopheles arabiensis from Ethiopia (2012–2016): a nationwide study for insecticide resistance monitoring

“…Between 2011 and 2015, bendiocarb (with deltamethrin in 2011–2012) was the insecticide of choice for PMI-supported IRS activities in Oromia Region, where low levels of mosquito resistance were initially detected in 2012. However, because bendiocarb was largely abandoned due to its short residual efficacy, relative to other organophosphates and carbamates [ 33 ], only moderate levels of resistance developed in a few areas. Concurrent propoxur spraying in 2012 was accompanied by the emergence of potential resistance in some An.…”