Submitted to: Entomological News
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/30/2006
Publication Date: 12/20/2006
Citation: Day, W.H., Tatman, K.M. 2006. Changes in abundance of native and adventive coccinellidae (coleoptera) in alfalfa fields, in Northern New Jersey (1993-2004) and Delaware (1999-2004). Entomological News 117: 491-502. Interpretive Summary: Four species of non-native coccinellids (lady beetles) have established themselves via shipping in the northeastern United States since 1970. During this period, four native lady beetles have become rare in alfalfa, and some have speculated that the foreign beetles caused this change. This field study was begun on three NW New Jersey farms in 1993, when only the first of the four non-native lady beetles was present and abundant, and continued until 2004. Samples were taken in alfalfa fields each week from May-July, and biweekly August-October. A similar study was done in NW Delaware from 1999-2004, using weekly samples in alfalfa. Considerable variation in lady beetle numbers, and to a lesser extent species, occurred over these years, demonstrating that many years of research are required to accurately measure population trends. The most abundant lady beetles at both locations were two native species (Coleomegilla maculate and Hippodamia parenthesis) and three non-native species (Propylea 14-punctata, Coccinella 7-punctata, and Harmonia axyridis). Four to five native lady beetles, and one non-native species, were rarely sampled at either location. Because all of the non-dominant native species were already uncommon in NJ in 1993,when only one non-native lady beetle was present and abundant, it was clear that competition with “new” lady beetle species was probably not the major reason for the decline of native species. The much earlier decrease in numbers of the pea aphid (the principal food of lady beetles in alfalfa), caused by parasitic wasps (Aphidius spp. introduced for biocontrol of this damaging aphid) was likely the cause of the reductions of these native lady beetles.
Technical Abstract: Weekly and biweekly sweep net collections were made near Blairstown, NJ and Newark, DE for 12 and 6 consecutive years, respectively. In New Jersey, only one non-native coccinellid (C. 7-punctata) species was common when this research was started in 1993, one (P. 14-punctata) had recently appeared, and two other foreign species (H. axyridis, H. variegata) 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, and Hippodamia parenthesis, and three adventive species, Propylea 14-punctata, Coccinella 7-punctata, and Harmonia axyridis. Six species were occasionally swept at Blairstown--one adventive species (H. variegata) and five native species (Cycloneda munda, Coccinella transversoguttata, C. trifasciata, Hippodamia convergens, and Brachiacantha ursina). 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 in New Jersey--indicating that the once-common H. convergens and several Coccinella species 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, which reduced pea aphid numbers, was likely responsible for decreasing coccinellid diversity in alfalfa. It is possible that competition by the adventive C.7-punctata also reduced some coccinellid species, but such data for the northeastern U.S. have not been published, to our knowledge.