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

The control of Simulium has 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 vector S. damnosum Theobald 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 in Simulium control 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 of Bacillus thuringiensis var. israelensis as a Simulium larvicide is reviewed in detail. The environmental impact of control of Simulium larvae, 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.

Dipteran predators of Simuliid blackflies: a worldwide review

“…In order to clarify a predator–prey relationship, surveys need to be made of developmental simuliid populations (Walsh, 1985), with appropriate statistical analyses, to determine the effects of predation upon the prey population. Laboratory experiments can give some indications, but the biotic and abiotic conditions are often not comparable with those found in the field.…”

Changes in feeding selectivity of freshwater invertebrates across a natural thermal gradient

“…The switch from feeding on sessile high profile to motile diatoms suggests a shift from active collector gathering to filter feeding behavior. Indeed, previous studies suggest that other Simulium species have the capability to feed by both collector gathering and filter feeding ( Burton 1973 ; Walsh 1985 ; Alder and McCreadie 1997 ). The latter may be a more energetically efficient feeding strategy in warmer environments because it is a more passive mode of capturing prey, thus expending less energy through movement and contributing to Simuliidae having one of the highest growth conversion efficiencies among freshwater invertebrates ( Cummins and Klug 1979 ).…”

“…The blackfly larva Simulium aureum Fries, 1824, may traditionally be thought of as a strict filter feeder, but has congeners that are able to collect small algal particles from the biofilm, i.e. collector gatherers ( Burton 1973 ; Walsh 1985 ; Alder and McCreadie 1997 ), and this behaviour has been regularly observed in the Hengill system (personal observation). The midgefly larva Eukiefferiella minor Edwards, 1929, is thought to be a largely generalist collector gatherer ( Henriques-Oliveira et al.…”

A Conceptual Model for the Estimation of the Sensitivity of Black Fly Larvae to Bacillus thuringiensis var. israelensis

“…Thus, the larval mortality should vary as a function of the amount of Bti actually ingested. Standad assays imply that ingestion sf Bti is simply a function of larvicide concentration and the contact time, and is independent of other factors (such as temperature, food concentration, or larval size), an assumption contradicted by observations on feeding rates of black fly larvae (Elsen and HCbmd 1979;Elsen 1980;H a t and Eatta 1985;Kurt& 1978;Lacey and Mulla 2975;Walsh 1985).…”