Evaluation of the Efficacy and Residual Activity of Some Candidate Larvicide Formulations for the Control of an Invasive Mosquito, Anopheles stephensi Liston (Diptera: Culidae) at Awash Sebat Kilo in Afar Region, Ethiopia.

Abstract

Malaria is transmitted between humans by the bite of adult female mosquitoes of the genus Anopheles. Despite huge efforts, malaria remains a global public health problem. Vector control tools such as indoor residual sprayings (IRS) and Insecticidal treated nets (ITNs) rely on chemical insecticides to control adult mosquitoes. The newly exotic invasive An.stephensi in Ethiopia poses additional challenge to malaria elimination agenda as it is resistant to most insecticide classes. Controlling immature stages of mosquitoes is equally important for the control of malaria vectors. SumiLarv 2MR is a matrix release specifically designed to be used in water storage vessels or water tanks while SumiLarv 0.5G is a granular formulation designed for open water sources and container treatments. Both SumiLarv 2MR and Sumilarv 0.5G contain pyriproxyfen (an insect growth hormone mimic) are novel larvicide formulations used for the control of mosquito larvae. Abate 1SG used widely as larvicide to control mosquitos’ vectors. In this study the efficacy and residual activity of SumiLarv 2MR, SumiLarv 0.5G and Abate 1SG larvicide were evaluated against An. stephensi at Awash Sebat Kilo in Afar Region, Ethiopia. One disc SumiLarv 2MR were applied into plastic containers each containing 100L, 250L and 500L from drinking water (tap water) each with four replicates were treated with 2g/disc (pyriproxyfen; 40mg/disc) (recommended dose). In parallel, plastic containers with 100L, 250L and 500L) of water without 2g/disc SumiLarv 2MR disc each with two replicates were set as control. In addition, 0.2g of Sumilarv 0.5G was applied to 100L of water in four replicates and 10g of Abate 1SG was applied to 100L of water in four replicates. In parallel, a container with 100L of water in two replicates for each formulation (Sumilarv 0.5G and Abate 1SG) were set as control. After the completion of the Study, the residual concentration of Pyriproxyfen left in each SumiLarv 2MR disc was also analyzed. The results of this study revealed that the residual efficacy of SumiLarv 2MR against An. stephensi larvae extended up to nine months (35 weeks). However, the residual efficacy of SumiLarv 0.5G and Abate 1SG performed only for seven and five weeks, respectively. Nine month old SumiLarv 2MR discs were left with almost 50% residual content of Pyriproxyfen showing the potential of SumiLarv 2MR residual efficacy for more additional time. Therefore, SumiLarv 2MR appeared to be an effective larvicide with longer residual efficacy against invasive An. stephensi in Ethiopia. Sumilarv 2MR is long residual activity more than nine month when compared with Sumilarv Abate 1SG to control an invasive Anopheles stephensi better to use for controlling Malaria Vector both in urban and rural areas