The ingestion and digestion of algal and other foods by larval black flies (Diptera: simuliidae) of Newfoundland

Thompson, Bruce Hunter (1989) The ingestion and digestion of algal and other foods by larval black flies (Diptera: simuliidae) of Newfoundland. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Feeding selectivity in larval simuliids of several Newfoundland species was studied by comparing relative abundances of algal taxa in the guts of field-collected larvae with those in the associated seston and periphyton. With the exception of the first instar of Prosimulium mixtum Syme & Davies, larvae of P. mixtum, Stegopterna mutata Malloch, Cnephia ornithophilia Davies et al., Simulium vittatum Zetterstedt, Simulium venustum Say and S. verecundum Stone & Jamnback utilized the seston almost exclusively for provision of food. No evidence was found to suggest that algal particles were selected on a qualitative basis, nor did the data indicate striking dissimilarities among species of similar physiological age, as to selectivity based on particle size. However, differing selectivities on the basis of particle size were observed among conspecific larvae of different physiological age. C. ornithophilia appeared to be exceptional, showing selectivity for relatively large diatom particles over much smaller bacterial particles, as compared to other species of larvae tested. Selectivity for particles within a certain intermediate size range (5-15 µm) was comparatively high for this species. -- Measurements of gut passage rates in the eurythermal S. vittatum indicated that feeding rates increased generally with increased temperature and particulate matter (PM) concentration. Feeding efficiency, however, decreased with increased PM concentration and with increased current velocity. The completeness of digestion, studied by using diatoms as indicators, increased generally with increasing temperature in S. vittatum and the warm stenothermal S. verecundum. In P. mixtum, a cold stenothermal species, the reverse temperature relationship was shown. Algae of different taxa varied markedly in susceptibility to digestion. -- Larvae of different species were capable of utilizing a wide variety of particulate foods, including algae, bacteria and detritus. In feeding trials, overall larval growth was highest when fed on diatoms, lowest when fed on leaf litter and intermediate when reared on green algae or bacteria. The nutritional importance of various classes of suspended particulate matter is a function of its availability in the seston, its susceptibility to ingestion, its inherent digestibility and its nutrient content. -- Key words: Simuliids; filter-feeding; selectivity; grazing; algae; bacteria; digestion; productivity; nutrition; feeding rates.

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