Degradation of insecticides used for indoor spraying in malaria control and possible solutions

Abstract

BackgroundThe insecticide dichloro-diphenyl-trichloroethane (DDT) is widely used in indoor residual spraying (IRS) for malaria control owing to its longer residual efficacy in the field compared to other World Health Organization (WHO) alternatives. Suitable stabilization to render these alternative insecticides longer lasting could provide a less controversial and more acceptable and effective alternative insecticide formulations than DDT.MethodsThis study sought to investigate the reasons behind the often reported longer lasting behaviour of DDT by exposing all the WHO approved insecticides to high temperature, high humidity and ultra-violet light. Interactions between the insecticides and some mineral powders in the presence of an aqueous medium were also tested. Simple insecticidal paints were made using slurries of these mineral powders whilst some insecticides were dispersed into a conventional acrylic paint binder. These formulations were then spray painted on neat and manure coated mud plaques, representative of the material typically used in rural mud houses, at twice the upper limit of the WHO recommended dosage range. DDT was applied directly onto mud plaques at four times the WHO recommended concentration and on manure plaques at twice WHO recommended concentration. All plaques were subjected to accelerated ageing conditions of 40°C and a relative humidity of 90%.ResultsThe pyrethroids insecticides outperformed the carbamates and DDT in the accelerated ageing tests. Thus UV exposure, high temperature oxidation and high humidity per se were ruled out as the main causes of failure of the alternative insecticides. Gas chromatography (GC) spectrograms showed that phosphogypsum stabilised the insecticides the most against alkaline degradation (i.e., hydrolysis). Bioassay testing showed that the period of efficacy of some of these formulations was comparable to that of DDT when sprayed on mud surfaces or cattle manure coated surfaces.ConclusionsBioassay experiments indicated that incorporating insecticides into a conventional paint binder or adsorbing them onto phosphogypsum can provide for extended effective life spans that compare favourably with DDT's performance under accelerated ageing conditions. Best results were obtained with propoxur in standard acrylic emulsion paint. Similarly, insecticides adsorbed on phosphogypsum and sprayed on cattle manure coated surfaces provided superior lifespans compared with DDT sprayed directly on a similar surface.

Production of the bioinsecticide Bacillus thuringiensis subsp. israelensis with deltamethrin increases toxicity towards mosquito larvae

“…Nevertheless, this explanation is unlikely for temephos and permethrin, which are stable for 2 weeks at 54°C (Aksoy et al 2007). Moreover, the toxicity of DDT and propoxur for mosquitoes does not seem to be significantly affected by high temperatures (Sibanda et al 2011). Further improvement in this production protocol (e.g.…”

“…Moreover, the toxicity of DDT and propoxur for mosquitoes does not seem to be significantly affected by high temperatures (Sibanda et al . ). Further improvement in this production protocol (e.g.…”

Insecticide resistance status of malaria vectorsAnopheles gambiae s.lof southwest Burkina Faso and residual efficacy of indoor residual spraying with microencapsulated pirimiphos-methyl insecticide

“…In addition to the insecticide physiological resistance, a variety of factors can affect the effectiveness of IRS. Indeed, residual life and efficacy of the insecticide used can vary according to the formulation, the quality of sprays, and the type of walls (cements, mud, wood) (Sibanda et al 2011, Djènontin et al 2013.…”

Sustainable malaria control: transdisciplinary approaches for translational applications

“…Alternatively, durable insecticide-treated wall linings (ITWLs), a recent product concept that combines aspects of LLINs and IRS, promise long-lasting residual efficacy, negating the need for repeated annual wall treatments as currently occurs with IRS. In combination with newly identified suitable insecticide alternatives using slow-release formulations [62,63], ITWL can be used as a substitute for IRS, since it allows protective containment of the insecticide in a polymer, resulting in a longer residual efficacy. Additionally, natural insecticides including permethrin or pyrethrin and essential oils such as thymoquinone, nootkatone and carvacol [32] should be explored if their residual period of use could be increased [33].…”