Abundance of some native coccinellines (Coleoptera: Coccinellidae) before and after the appearance ofCoccinella septempunctata

Abstract

AbstractThe seven-spotted lady beetle,Coccinella septempunctataL., was first reported in Manitoba in 1988. The effect of this introduced species on the relative abundance of the more common native coccinellines was determined from D-Vac Insect Net®and sweepnet samples in alfalfa in 1983–2001, by sweepnet and visual sampling in field crops and other vegetation in 1989–2001, and by transect sampling of aggregations of coccinellines in spring and autumn on the shore of Lake Manitoba from 1989 to 2001. The trends of annual changes in the abundance of six species in southern Manitoba were similar, whether based on the mean density per 200 sweeps in alfalfa or on their relative abundance in alfalfa, on other vegetation, and in aggregations on the beach. Before 1988,Hippodamia tredecempunctata tibialis(Say),Coccinella transversoguttata richardsoniiBrown, andHippodamia convergensGuerin were the most abundant species, followed byHippodamia parenthesis(Say) andCoccinella trifasciata perplexaMulsant. By 1992,C. septempunctatahad become the dominant species, butH. tredecempunctatahas since been the dominant species in most collections. The relative abundance ofC. transverso guttata,H. convergens,H. parenthesis, andC. trifasciatahas decreased since the establishment ofC. septempunctata. The decline in abundance of these species seems to be caused by their competitive displacement byC. septempunctata. Their displacement also might be a contributing factor in the slight increase in abundance ofH. tredecempunctatabecauseC. septempunctatamay compete less directly with this species than with other native coccinellines.