CHANGES IN ABUNDANCE OF NATIVE AND ADVENTIVE COCCINELLIDAE (COLEOPTERA) IN ALFALFA FIELDS, IN NORTHERN NEW JERSEY (1993–2004) AND DELAWARE (1999–2004), U.S.A

Abstract

Weekly and biweekly sweep net collections were made near Blairstown, New Jersey, and Newark, Delaware (both in the U.S.A.), for 12 and 6 consecutive years, respectively. At Blairstown, only one non-native coccinellid [Coccinella septempunctata (L.)] was common when this research was started in 1993, one [Propylea quatuordecimpunctata (L.)] had recently appeared, and two others [Harmonia axyridis (Pallas), Hippodamia variegata (Goeze)] were detected later during the 12-year study. All of these four species were adventive, having established themselves through commerce, three species at inland ports, and one near a coastal seaport. The most numerous adult lady beetles at both locations were two native species, Coleomegilla maculata (F.) and Hippodamia parenthesis (Say), and three adventive species, P. quatuordecimpunctata, C. septempunctata, and H. axyridis. Six species were occasionally swept at Blairstown - one adventive species (H. variegata) and five native species [Cycloneda munda (Say), Coccinella transversoguttata Mulsant, C. trifasciata Mulsant, Hippodamia convergens Guerin, and Brachiacantha ursina (F.)]. All but the last species were also found at Newark. Lady beetle numbers varied considerably from year to year at both locations, demonstrating that long-term (10 years or more) research is required to correctly identify population trends. No coccinellid species decreased during the 12-year study at Blairstown—indicating that the once-common H. convergens and several species of Coccinella had become rare before the study started in 1993, and before three of the four adventive lady beetles had become numerous. The previous establishment of exotic parasites, previously reported to have reduced pea aphid numbers, was likely indirectly responsible for decreasing coccinellid diversity in alfalfa. Competition by the adventive C. septempunctata may also have reduced some coccinellid species prior to 1993, but such data for the northeastern U.S.A. have not been published, to our knowledge.