Drift behaviour and microhabitat selection in the preimaginal stages of Simulium chutteri (Diptera Simuliidae)

Abstract

The aquatic stages of the cattle biting pest, Simulium chutteri Lewis utilize river flow in their dispersal and colonization behaviour. Peaks of drifting activity in S . chutteri larvae occurred in the early morning and late afternoon. It is deduced that female flies scatter eggs onto slow flowing waters upstream of rapids . Larvae hatch from drifting eggs and colonize substrates in slower flowing regions upstream of rapids, while later stage instars move into faster flowing regions within rapids where they complete their development . This microhabitat selection by S. chutteri leads to rapid attainment of large population sizes in suitable sections of river and reduces competition between different stage larvae . In their utilization of a variety of microhabitats the larvae of this species differ from co-existing simuliid species which restrict developmental stages to single habitats .Catastrophic drift was recorded for S . chutteri larvae and could be a mechanism to regulate population size.Drift of simuliid larvae off rapids was not related to benthic population densities in the rapids and was therefore not due to excessive production . It is concluded that larval drift off rapids is related to habitat disturbances associated with water flow fluctuations and the activity of aquatic predators and other animals .The distribution of S. chutteri in the Vaal River is restricted by oviposition requirements of the adult female. Knowledge of drift behaviour and water flow requirements of Simuliidae have been applied to manage the population size of S. chutteri in the Vaal River. Hydrobiologia 133, 143-154 (1986) .

A model to predict outbreak periods of the pest blackfly Simulium chutteri Lewis (simuliidae, Diptera) in the Great Fish River, Eastern Cape province, South Africa

“…Very few examples on the use of flow manipulation to reduce pest blackfly populations were found in the literature, although they were already identified and proposed as an effective control option as early as the 1970s (Waters, 1972). Examples of flow manipulation for controlling larval blackfly were found from the former USSR (Dubitskii, 1981) and South Africa (Howell et al, 1981;de Moor, 1982bde Moor, , 1997Car, 1983;de Moor et al, 1986). This is surprising given that changes in water flow have been shown to greatly influence blackfly larval densities (see for example de Moor, 1994b;Zhang et al, 1998).…”

“…Flow manipulation assumes the existence of impoundments upstream to simuliid breeding sites (Car, 1983;de Moor, 1997), as with Elandsdrift Dam. There is consensus that the most effective window time period to control blackfly is winter, when the majority of the population is in the larval or pupal phase, which if left uncontrolled can lead to major spring outbreaks (de Moor, 1982b(de Moor, , 1997Car, 1983;de Moor et al, 1986;Palmer, 1997). Winter shutdowns of flow to dry out blackfly larvae and pupae by exposing substrate (de Moor, 1982b(de Moor, , 1997O'Keeffe and de Moor, 1988) target the period of maximum annual population growth, and avoid conflict with irrigation demand (O'Keeffe and de Moor, 1988).…”

A preliminary assessment of the effects of a small south african inter-basin water transfer on discharge and invertebrate community structure

“…In terms of collector/grazers, caenid ephemeropterans (Merritt and Cummins, 1984) occurred only below the IBT, while the specialist collector/filterers, the Simuliidae, also showed some response below the siphon, reaching relatively high numbers in May (Table II). Interestingly, the simuliids in the Berg River did not respond to anywhere near the extent recorded for the Great Fish River by O'Keeffe and de Moor (1988), or for that matter for any other regulated river system in southern Africa (Chutter, 1967(Chutter, , 1968de Moor, 1982;de Moor et al, 1986;Car and de Moor, 1984;Palmer, 1991). In the case of the Vaal River, Chutter (1967Chutter ( , 1968 found that densities of the pest blackfly species, S. chutteri, were highest when flow fluctuations were greatest below the Vaalhartz Diversion Weir.…”

Evaluation of the impact of Bacillus thuringiensis serovar israelensis and Temephos, used for the control of Simulium (Chirostilbia) pertinax Kollar, 1832 (Diptera, Simuliidae) on the associated entomofauna, Paraty, state of Rio de Janeiro, Brazil

“…The latter did not observe any reduction in the Chironomidae population after using a Bti concentration of 1.6 ppm applied during 10 min. On the other hand, Dejoux et al (1985), in the Ivory Coast, de Moor et al (1986), in South Africa, and Molloy (1992) in the United States, reported a population reduction by using the same concentration of Bti. Regarding the species adapted to lentic environments, field and laboratory experiments have demonstrated the high susceptibility of certain chironomid species to Bti formulations (Rodcharoen et al 1991, Kondo et al 1992, Charbonneau et al 1994.…”

“…Similar results were reported by Merrit et al (1989), concerning specifically the family Hydropsichidae. On the other hand, Dejoux et al (1985), and de Moor et al (1986), working in the African continent, reported an effect of Bti on these insects. It is possible that the effects were due formulation components rather than toxins of the bacterium.…”