The feeding behaviour ofSimuliumlarvae, and the development, testing and monitoring of the use of larvicides, with special reference to the control ofSimulium damnosumTheobald s.l. (Diptera: Simuliidae): a review

Abstract

AbstractThe control ofSimuliumhas always relied largely on the use of insecticides against the larvae, and this is the case in the current large-scale Onchocerciasis Control Programme against the vectorS. damnosumTheobald in West Africa. Resistance to temephos has occurred in some vector species, and it is necessary to find alternatives to this preferred larvicide. In order to provide a frame of reference for the development of new larvicides or formulations, the literature relating to larval filter-feeding behaviour is first reviewed in detail. Then the physico-chemical conditions in larval habitats are outlined. The types of formulations and classes of insecticide used inSimuliumcontrol are considered, with particular attention being given to emulsifiable concentrate formulations and the reasons for their effectiveness. Particulate formulations, which have been recommended on environmental grounds, are also discussed. Techniques used in the screening of larvicides are considered, and it is concluded that flow-through systems are necessary; mini-gutter tests conducted using water and fauna from rivers to be treated are to be strongly preferred, followed by stream trials. Knowledge ofBacillus thuringiensisvar.israelensisas aSimuliumlarvicide is reviewed in detail. The environmental impact of control ofSimuliumlarvae, both in the tropics and the temperate zone, is extensively reviewed. Throughout, key features which might lead to improved larvicide formulations and testing procedures, together with serious gaps in our knowledge are emphasized.