Aquatain® Mosquito Formulation (AMF) for the control of immature Anopheles gambiae sensu stricto and Anopheles arabiensis: dose-responses, persistence and sub-lethal effects.

Steven W Lindsay,Oscar Mbare,Ulrike Fillinger

doi:10.1186/1756-3305-7-438

Abstract

BackgroundPersistent monomolecular surface films could benefit larval source management for malaria control by reducing programme costs and managing insecticide resistance. This study evaluated the efficacy of the silicone-based surface film, Aquatain® Mosquito Formulation (AMF), for the control of the Afrotropical malaria vectors, Anopheles gambiae sensu stricto and Anopheles arabiensis in laboratory dose–response assays and standardized field tests.MethodsTests were carried out following guidelines made by the World Health Organization Pesticide Evaluation Scheme (WHOPES). Sub-lethal effects of AMF were evaluated by measuring egg-laying and hatching of eggs laid by female An. gambiae s.s. that emerged from habitats treated with a dose that resulted in 50% larval mortality in laboratory tests.ResultsBoth vector species were highly susceptible to AMF. The estimated lethal doses to cause complete larval mortality in dose–response tests in the laboratory were 1.23 (95% confidence interval (CI) 0.99-1.59) ml/m2 for An. gambiae s.s. and 1.35 (95% CI 1.09-1.75) ml/m2 for An. arabiensis. Standardized field tests showed that a single dose of AMF at 1 ml/m2 inhibited emergence by 85% (95% CI 82-88%) for six weeks. Females exposed as larvae to a sub-lethal dose of AMF were 2.2 times less likely (Odds ratio (OR) 0.45, 95% CI 0.26-0.78) to lay eggs compared to those from untreated ponds. However, exposure to sub-lethal doses neither affected the number of eggs laid by females nor the proportion hatching.ConclusionAMF provided high levels of larval control for a minimum of six weeks, with sub-lethal doses reducing the ability of female mosquitoes to lay eggs. The application of AMF provides a promising novel strategy for larval control interventions against malaria vectors in Africa. Further field studies in different eco-epidemiological settings are justified to determine the persistence of AMF film for mosquito vector control and its potential for inclusion in integrated vector management programmes.

Highlights

Persistent monomolecular surface films could benefit larval source management for malaria control by reducing programme costs and managing insecticide resistance
We aimed to supplement the available knowledge by testing the efficacy of Aquatain® Mosquito Formulation (AMF) for the control of An. gambiae sensu stricto and An. arabiensis in Phase I and Phase II trials following the standardized procedures by the World Health Organization Pesticide Evaluation Scheme (WHOPES) [32]
Dose–response tests Larval mortality was similar in the three experimental rounds for each mosquito species; rounds were pooled for each mosquito species for calculation of mean larval mortality and effective lethal doses

Summary

Introduction

Persistent monomolecular surface films could benefit larval source management for malaria control by reducing programme costs and managing insecticide resistance. Unlike petroleum-based oils and other control agents, MMFs are not toxic to immature mosquitoes [19,20] Their mode of action is physical, rather than chemical, and they work by lowering the water surface tension that affects all stages of the mosquito life-cycle; it is ovicidal, larvicidal, pupicidal and adulticidal [17,19]. The reduced surface tension wets and drowns eggs, suffocates larvae and pupae and kills emerging and ovipositing females by drowning [19,21] This is an advantage over conventional insecticides that are only effective against larvae [22] or pupae [23]. The physical mode of action reduces the chance of mosquitoes developing resistance [24]

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