RECENT PRESENTATIONS
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North American Benthological Society, 1993, Calgary.
FLOW PATTERNS AROUND PUPAL GILLS OF NET-WINGED MIDGES (DIPTERA: BLEPHARICERIDAE): POSSIBLE IMPLICATIONS FOR RESPIRATION.
Gregory D. W. Pommen and Douglas A. Craig,
Department of Entomology, University of Alberta, Edmonton, CANADA T6G 2E3.
Gills of Blephariceridae pupae show a great variety of structure, ranging from robust lamellae to pads of spines. All gills appear to operate on the principle of an "incompressible gill" - a plastron. Previous work on gills of Simuliidae pupae by Eymann (1991) showed that the pupa acted as a bluff body producing paired vortices downstream of the gill position. He concluded that the vortices were in some manner involved in enhancing respiration. Examination of flow around of Blephariceridae pupae showed that it was similar to Simuliidae pupae, but unexpectedly, water did not usually pass directly through the gill lamellae. Observations on live pupae showed that bubbles of air were produced on a regular basis from the plastron of the gill. It is concluded that the higher velocity in the vortices produces low pressure sufficient to decrease the solubility of air in the water and enhance the ability of the plastron to take up gas. Hence, direct water flow through the gills may not be necessary. A known example of high velocity producing low pressure sufficient to outgas water for respiration in the beetle Potamodytes tuberosum will be used to support this conclusion.
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Entomological Society of Canada, Winnipeg, October, 1994.
FORM AND FUNCTION OF NET-WINGED MIDGE PUPAL GILLS (DIPTERA: BLEPHARICERIDAE): IMPLICATIONS FOR RESPIRATION.
Gregory D. W. Pommen and Douglas A. Craig,
Department of Biological Sciences, University of Alberta, Edmonton, CANADA T6G 2E9.
Blephariceridae pupal gills show great variety in structure. Flow around gills produces vortices, known regions of low pressure. This probably assists the plastron of the gill. That high velocity produces low pressure sufficient to outgas water for respiration in the beetle Potamodytes tuberosum is used to support this conclusion.
ACCELERATIVE ESCAPE MOTIONS IN BAETIS TRICAUDATUS (BAETIS: EPHEMEREOPTERA)
Douglas. A. Craig,
Department of Biological Sciences, University of Alberta, Edmonton, T6G 2E9.
Highspeed digital video recordings were used to examine the escape behaviour of Baetis tricaudatus larvae. Extreme body contortions commenced the locomotion sequence. Body undulations were cetacean. Analysis of the recordings showed that accelerations of up to 26.0 m/s/s were achieved by 8.0 mm larvae.
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American Society of Zoologists, January, 1995, St Louis, Missouri.
AQUATIC INSECT FEEDING:ANALYSIS WITH MICROCINEMATOCGRAPHY AND VIDEO
Merritt, R. W. and D. A. Craig,
Michigan State University, East Lansing and University of Alberta, Edmonton Canada.
Filter feeding aquatic insects have evolved active and passive methods to remove particulate matter from suspension. Passive methods used by Black Flies (Diptera: Simuliidae), depend on existing currents to bring food to the animal, while active filter feeding in mosquitoes (Diptera:Culicidae) involves energy expenditure to create feeding currents. The mouthparts that larval black flies use for filter feeding are the labral fans, mandibles and maxillae. Different species of mosquitoes use different morphological structures and feeding modes (e.g. filtering, suspension feeding, browsing, interfacial feeding) in food acquisition. During the last few years, we have examined the functional feeding morphology of larval black flies and mosquitoes using videotape recordings, high-speed microcinematography, and SEM to try and understand how feeding morphology and mechanismss are interrelated in these two groups.
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North American Benthological Society, 1995, Colorado.
LABORATORY STUDIES ON DIRECT UPTAKE OF DISSOLVED ORGANIC MATTER (DOM) BY LARVAL BLACK FLIES (DIPTERA: SIMULIIDAE).
K.M. Fry1, J.J.H. Ciborowski2 & D.A. Craig1.
1Dept. Biological Sciences, Univ. Alberta, Edmonton AB, T6G 2E9, and 2Dept. Biological Sciences, Univ. Windsor, Windsor, ON, N9B 3P4.
Black fly larvae often dominate habitats containing abundant DOM but limited particulate matter. To determine if larvae can ingest DOM, we reared Simulium larvae in stir-bar driven rearing chambers containing synthetic river water and/or brewer's yeast and/or DOM (an autoclaved, 0.22 um-filtered, aqueous extract of moss). Growth in control (water only) trials was insignificant, but larvae grew by up to 10% when fed 3 mg/L yeast and/or 20 mg/L DOM. Additional experiments were performed to directly demonstrate DOM in the guts of larvae. Forty larvae in synthetic river water were fed red Dayglo dye particles, for 10 min and placed in clean water for 30 min. Groups of 10 larvae were then transferred to rearing chambers containing water with 0, 20, 60 or 120 mg/L DOM for 8 h. All larvae were then fed yellow Dayglo particles for 10 min, washed in clean water and fixed in alcoholic Bouins. Larvae were sectioned and stained with 1% Alcian Blue at pH 2.5 (a dye specific for sulphate and carboxyl groups, which are constituents of many carbohydrates and mucopolysaccharides) to show presence or absence of DOM in the guts between the Dayglo dye markers. Microscopic examination of larval guts revealed materials interpretable as DOM in the higher dosage DOM treatments. However, results were equivocal because larvae in all treatments had reingested positively-staining particulate faecal material. Experiments in progress using individual larvae in a flow-through system will resolve this problem.
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