Non-native lady beetles: a diversity of outcomes

Authors: Hesler, Louis

Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 2/12/2016
Publication Date: 4/18/2016
Citation: Hesler, L.S. 2016. Non-native lady beetles: a diversity of outcomes. Internatioinal Congress of Entomology / Entomol. Soc. Amer. meeting, Sep. 30, 2016, Orlando FL.

Interpretive Summary: Two non-native species of lady beetles have established over the last 30 years in South Dakota: sevenspotted lady beetle (C7) in 1987, and multicolored Asian lady beetle in 1996. Two native species of lady beetles disappeared from eastern South Dakota soon after the establishment of C7. Thus, long-term monitoring of lady beetle populations is vital to determining colonization patterns of the non-native species and in assessing the potential for further impact on native lady beetles. In this study, five kinds of field-crop plots (winter and spring small grains, alfalfa, corn, and soybean) and relict prairie were sampled from 2007 through 2016 in east-central South Dakota to determine relative abundances of native and non-native lady beetles. Results showed C7 was generally abundant in alfalfa, winter wheat and soybeans in most years, whereas multicolored Asian lady beetle was abundant primarily in soybeans. The non-native variegated lady beetle was first detected in 2010 at the study site, but it was sampled at very low numbers thereafter. The two types of native lady beetles that disappeared following C7 establishment were not found in this study, but other native lady beetle species remained moderately abundant among crops. These results underscore the importance of empirical studies in determining diverse outcomes from the establishment of non-native lady beetles.

Technical Abstract: Introduction: Various lady beetle species have expanded their geographic ranges following intentional or accidental introduction and subsequent establishment within new regions. In many cases, this has been accompanied by declines in native lady beetles. Long-term monitoring of lady beetle populations is vital to determining colonization patterns of non-native species and in assessing the ensuing impact on native species. Two non-native species of lady beetles have established over the last 30 years in South Dakota, USA: Coccinella septempunctata L., first detected in 1987, and Harmonia axyridis (Pallas), first detected in 1996. Methods: In a long-term study, five kinds of field-crop plots (winter and spring small grains, alfalfa, corn, and soybean) and prairie were sampled from 2007 through 2016 in east-central South Dakota to determine relative abundances of native and non-native lady beetles and to assess their habitat use patterns. Results/Conclusion: Results showed diverse patterns in colonization and relative abundances of non-native species among habitats. Coccinella septempunctata was generally abundant in alfalfa, winter wheat and soybeans in most years, whereas H. axyridis was abundant primarily in soybeans. Hippodamia variegata (Goeze) was first detected in 2010 and sampled in low numbers thereafter. Two native lady beetles, Hippodamia convergens (Guerin) and Coleomegilla maculata lengi Timberlake, remained moderately abundant among crops, and several other species of native lady beetles persisted at low levels during the study. These results underscore the importance of empirical studies in determining diverse outcomes from establishment of non-native lady beetles.