A Study of the Population of Insects Emerging as Adults from Medway Creek at Arva, Ontario

Abstract

Between April 14 and October 15, 1959, 8,399 adult insects were trapped in five tent-traps set out on Medway Creek. The orders represented were Ephemeroptera (0.04%), Trichoptera (0.3%), Hemiptera (0.04%), Coleoptera (0.05%), Diptera (99.56%), Hymenoptera (0.01%). Midges of the family Chironomidae constituted 99.62% of the Diptera. Other families of Diptera, present in much smaller numbers, were Ceratopogonidae, Mycetophilidae, Empididae, Ephydridae, Borboridae, Lauxaniidae and Muscidae. The numbers and seasonal occurrences, including times of maximum emergence, are reported for each species. Medway Creek flows through London Township, Middlesex County, Ontario and joins the Thames River at the city of London. About one mile north of London, at the village of Arva on Provincial Highway No. 4, the creek has been dammed to, provide a power supply for a flour mill (Fig. 1). Above the dam the creek widens out to form a narrow lake extending between the Seventh and Eighth Concession Roads of London Township. At its lower end the lake is surrounded by fields and at its upper end by deciduous woods. There are two bends in the lake, an upper and a lower one. In the upper bend there are two narrow islands which divide the creek into three channels. Above the upper bend the creek has several narrow bays extending into the surrounding woods. During the summer of 1959 a studv of the aquatic insects emerging from the creek was undertaken and the present paper is a report on this project. Acknowledgment.-The wvriter gratefully acknowledges the assistance of Mr. A. G. Carmichael and Mr. J. Shute who aided during the summer of 1959 in collecting insects from traps, in sorting and counting specimens and in recording data. Dr. E. Shute provided docking facilities for the boat and permitted access to the collection area. The map in Figure 1 was traced from an aerial photograph provided by the London and Suburban Planning Board. METHODS The emerging insects were trapped in five tent-traps anchored on the water at five locations on the creek (Fig. 1, 1-5). Trap 1 was located in the middle of the creek a few feet above the dam. Trap 2 was in the center of a wide bay in the lower bend of the creek. Trap 3 was in the middle of the creek midway between the upper and lower bends of the creek. Trap 4 was in the most easterly of the three channels in the upper bend. Trap 5 was just above the upper bend. Each trap enclosed four square feet of water surface. The structure of a trap and the methods of collecting insects from it are described by Judd (1957). 463 This content downloaded from 157.55.39.88 on Thu, 21 Jul 2016 04:46:23 UTC All use subject to http://about.jstor.org/terms 464 THE AMERICAN MIDLAND NATURALIST 68(2) On February 25 the whole surface of the lake was frozen over and no water was flowing over the dam. On March 1 the whole surface was still frozen over and water was flowing freely over the whole width of the dam from under the edge of the ice. These conditions prevailed until March 30 with the whole lake still frozen over except at the edge of the dam. The torrent of water passing over the dam during this period is pictured in a photograph in the London Free Press of March 20, 1959. After March 30 thawing occurred rapidly and by April 2 the whole creek was free of ice and water was flowing freely through it. The traps were anchored in place on April 14 and removed from the water on October 15. In the period between these dates the traps were visited each day bv boat and insects were collected from them. The depth of water at each trap was also measured each day.