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

Abstract

Background: Persistent 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.

Methods: Tests 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.

Results: Both 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.

Conclusion: AMF 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.

Figure 1

Standardized field test set up. Netting-covered emergence trap on top of artificial pond.

Figure 2

Mean mortality of larvae exposed to increasing doses of AMF in dose–response tests. Error bars represent 95% confidence intervals.

Figure 3

Weekly emergence of An. gambiae s.l. from control (C) and treatment (T) in standardized-field tests. Error bars represent 95% confidence intervals.