Quantitative studies on the eggs of <i>Simulium (Simulium) ornatum</i> Meigen and <i>Simulium (Wilhelmia) equinum</i> L. in a chalk stream in southern England

Welton, J. S.; Bass, J. A. B.

doi:10.1111/j.1365-2311.1980.tb01126.x

Cited by 15 publications

(6 citation statements)

References 18 publications

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“…Other factors being equal, it is likely that ovipositing aquatic insects choose egg-laying sites where temperature conditions are optimal for subsequent development. Welton and Bass (1980) have, for example, demonstrated signi®cant dierences in levels of oviposition by Simulium equinum and Simulium ornatum in relation to the aspect, and by implication exposure to solar heating and water temperature, of the river margin. The eggs of these insects are deposited on marginal vegetation, which often consists of grasses, and lie just at or beneath the water surface, so that dierences in temperature encountered above and below¯oating and marginal vegetation in the study rivers could be signi®cant.…”

Section: Water Columnmentioning

confidence: 99%

Microthermal gradients and ecological implications in Dorset rivers

Clark

Webb

Ladle

1999

Hydrological Processes

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Microthermal gradients, involving signi®cant variations in temperature over distances of a few centimetres to a few metres, were investigated in the water column and substratum of the River Frome and Bere Stream in Dorset, UK, which are groundwater dominated streams fed by chalk aquifers. In many of the sections surveyed, strong lateral contrasts of up to c. 7 8C were evident as a consequence of solar heating of shallow channel margin zones and thin surface layers isolated by¯oating vegetation from the main body of¯ow. Shading by instream, emergent and riparian vegetation, and by river banks also caused signi®cant microthermal gradients in the water column. Detailed logging of temperatures in the substratum at selected sites revealed damping of variation with increasing depth below the bed surface, seasonal reversal in bed temperature gradients and considerable local variation in the substratum temperature pro®les of a pool-rie sequence. The latter did not conform to the pattern expected from advective heat transfer associated with downwelling of water at the rie head and upwelling at the tail, and measurements of interstitial¯ow velocities and particle size suggested more complex¯ow circulation and heat transfer. There was some evidence that the microthermal gradients identi®ed were of ecological signi®cance.

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Section: Water Columnmentioning

confidence: 99%

Microthermal gradients and ecological implications in Dorset rivers

Clark

Webb

Ladle

1999

Hydrological Processes

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“…The reduction in depth alone may expose eggs of invertebrates (e.g. Simuliidae) and fish (Rutilus rutifus L.) to drying (Welton and Bass, 1980;Mills, 1981) and an increase in velocity and general disturbance will increase turbidity and result in the movement and redistribution of faunal communities (Kern-Hansen and . Note that the graph in Figure 8B does not show the transient effects that occur during and immediately after cutting.…”

Section: Weed Cuttingmentioning

confidence: 99%

Implications of the annual macrophyte growth cycle on habitat in rivers

Hearne

Armitage

1993

Regul. Rivers: Res. Mgmt.

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The continuity equation, Manning's equation and an empirically determined relationship between channel roughness and the biomass of macrophytes were used to simulate the effects of weed growth in contrasting channels. Two indices of wetted available habitat, velocity and depth were chosen to illustrate the role of macrophyte in maintaining and modifying instream habitat with particular reference to chalk streams. Plant growth maintained depth within the channels and its effect was modified by channel shape and slope. Weed cutting resulted in very sudden changes in depth and velocity and the loss of a large volume of water from the river. The results indicate that macrophyte growth could be used to maintain wetted habitat while allowing more abstraction, but more data are required on the long-term effects of implementing such policies.

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“…They oviposit on the soil surface and in desiccation cracks. They are either immersed or are in situations with a very high relative humidity and do not hatch if desiccated even for quite short periods (Welton & Bass 1980;Riihm 1983). Eggs may develop without delay or have an intrinsic delay (Grenier 1949;Davies 1963;Colbo & Wotton 1981).…”

Section: Introductionmentioning

confidence: 99%

Distribution of Oviposition Sites and Characteristics of Egg Development in the 'Blandford Fly' Simulium posticatum (Diptera: Simuliidae)

Welton¹,

Bass²,

Ladle³

et al. 1987

The Journal of Applied Ecology

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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. British Ecological Society is collaborating with JSTOR to digitize, preserve and extend access to Journal of Applied Ecology. SUMMARY(1) Eggs of Simuliumposticatum have previously been found in bankside soil above the water surface. This study investigated the distribution of oviposition sites on the River Stour, U.K., in relation to a local medical problem caused by the bites of the females.(2) The characteristics of the river bank were noted. Sites with a vertical bank profile and loamy soil in the shade were favoured by the females. Aspect and water velocity were not related to oviposition site.,(3) Four weeks of exposure to low temperature was required to break the diapause of the eggs and the minimum total time taken to hatching was 8 weeks. High temperatures, after the diapause had been broken, inhibited hatching (4% hatch after 9 days at 14WC, compared with 48% at 5QC).(4) Larvae were seen to hatch on damp soil but hatching success was greater among eggs immersed in water. Mortality of first-instar larvae was low at 5?C (6% after 7 days, compared with > 70% at 9?C and 14?C). This may be an adaptation to the time required to find a suitable feeding site at the ambient temperature of the river.(5) Eggs were not resistant to desiccation even though they normally remain in soil from early summer to the following February. At relative humidities of < 87%, more than 70% of S. posticatum eggs were distorted after 3 days, although the proportion of S. ornatum eggs distorted by this treatment was much greater ( > 97%).(6) It was concluded that high relative humidity and the presence of capillary water in soil produced favourable conditions for egg development and survival.

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Quantitative studies on the eggs of Simulium (Simulium) ornatum Meigen and Simulium (Wilhelmia) equinum L. in a chalk stream in southern England

Cited by 15 publications

References 18 publications

Microthermal gradients and ecological implications in Dorset rivers

Microthermal gradients and ecological implications in Dorset rivers

Implications of the annual macrophyte growth cycle on habitat in rivers

Distribution of Oviposition Sites and Characteristics of Egg Development in the 'Blandford Fly' Simulium posticatum (Diptera: Simuliidae)

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