Dose–response tests and semi-field evaluation of lethal and sub-lethal effects of slow release pyriproxyfen granules (Sumilarv®0.5G) for the control of the malaria vectors Anopheles gambiae sensu lato

Abstract

BackgroundRecently research has shown that larviciding can be an effective tool for integrated malaria vector control. Nevertheless, the uptake of this intervention has been hampered by the need to re-apply larvicides frequently. There is a need to explore persistent, environmentally friendly larvicides for malaria vector control to reduce intervention efforts and costs by reducing the frequency of application. In this study, the efficacy of a 0.5% pyriproxyfen granule (Surmilarv®0.5G, Sumitomo Chemicals) was assessed for the control of Anopheles gambiae sensu stricto and Anopheles arabiensis, the major malaria vectors in sub-Saharan Africa.MethodsDose–response and standardized field tests were implemented following standard procedures of the World Health Organization’s Pesticide Evaluation Scheme to determine: (i) the susceptibility of vectors to this formulation; (ii) the residual activity and appropriate retreatment schedule for field application; and, (iii) sub-lethal impacts on the number and viability of eggs laid by adults after exposure to Sumilarv®0.5G during larval development.ResultsAnopheles gambiae s.s. and An. arabiensis were highly susceptible to Sumilarv®0.5G. Estimated emergence inhibition (EI) values were very low and similar for both species. The minimum dosage that completely inhibited adult emergence was between 0.01-0.03 parts per million (ppm) active ingredient (ai). Compared to the untreated control, an application of 0.018 ppm ai prevented 85% (95% confidence interval (CI) 82%-88%) of adult emergence over six weeks under standardized field conditions. A fivefold increase in dosage of 0.09 ppm ai prevented 97% (95% CI 94%-98%) emergence. Significant sub-lethal effects were observed in the standardized field tests. Female An. gambiae s.s. that were exposed to 0.018 ppm ai as larvae laid 47% less eggs, and females exposed to 0.09 ppm ai laid 74% less eggs than females that were unexposed to the treatment. Furthermore, 77% of eggs laid by females exposed to 0.018 ppm ai failed to hatch, whilst 98% of eggs laid by females exposed to 0.09 ppm ai did not hatch.ConclusionAnopheles gambiae s.s. and An. arabiensis are highly susceptible to Sumilarv®0.5G at very low dosages. The persistence of this granule formulation in treated habitats under standardized field conditions and its sub-lethal impact, reducing the number of viable eggs from adults emerging from treated ponds, enhances its potential as malaria vector control tool. These unique properties warrant further field testing to determine its suitability for inclusion in malaria vector control programmes.

Soil presence reduces the control effectiveness of a slow‐release formulation of pyriproxyfen on Aedes aegypti (Diptera: Culicidae) larvae

“…There was a change in adult emergence behaviour at week 12, which may indicate that the slow‐release devices are effective for close to 3 months. This persistence is higher than other formulations, including granular ones . An initial delay in inhibition was observed in the three first weeks of our experiments in vases with soil.…”

Biological Activity of Sumilarv 0.5G against Anopheles gambiae sensu stricto and Anopheles arabiensis in Northern Tanzania

“…33,51 Overall, it can be concluded from previous and our own study that the efficacy and residual activity of different pyriproxyfen-containing products depends on the formulation, dose, habitat types, and vector species. 36,46 We did not observe that the efficacy of Sumilarv 0.5G is reduced in turbid water, as reported by Mbare et al 43 Some of the turbidity observed in that study might have been due to algae and bacteria growing in the established habitats. It is possible that the debris absorbed some of the active ingredients of the Sumilarv 0.5G, reducing its efficacy.…”

Exploring the potential of using cattle for malaria vector surveillance and control: a pilot study in western Kenya

“…arabiensis Mbita strain were obtained for bioassays from the icipe-TOC mosquito insectary where they were reared following standard procedures [36]. The females were 3–5 day-old and had never fed on blood; they were starved of sugar from noon on the day of their exposure to cattle.…”