Declining abundance of Coccinellidae (Coleoptera) among crop and prairie habitats of eastern South Dakota, USA

Authors: Hesler, Louis; Beckendorf, Eric

Submitted to: Frontiers in Conservation Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/13/2021
Publication Date: 9/17/2021
Citation: Hesler, L.S., Beckendorf, E.A. 2021. Declining abundance of Coccinellidae (Coleoptera) among crop and prairie habitats of eastern South Dakota, USA. Frontiers in Conservation Science. 2. Article 742036. https://doi.org/10.3389/fcosc.2021.742036.
DOI: https://doi.org/10.3389/fcosc.2021.742036

Interpretive Summary: Lady beetles serve as major predators of aphids and other pests of field crops. Several native lady beetle species in North America have declined in association with the introduction of invasive species of lady beetles. In particular, populations of three native species declined drastically (transverse lady beetle) or effectively disappeared (twospotted lady beetle and ninespotted lady beetle) from agricultural landscapes in eastern South Dakota, U.S.A., following establishment of the invasive sevenspotted lady beetle in the 1980s. Since then, two other non-native lady beetles (multicolored Asian lady beetle and variegated lady beetle) have established in eastern South Dakota, but long-term analysis of their impact on the aphidophagous lady beetle guild is lacking. This paper summarizes long-term results from 14 years (2007-2020) of sampling lady beetles by sweepnet and timed searches in five field crops and restored prairie in eastern South Dakota. In all, 17,099 predatory lady beetles comprising 10 species were sampled. The sevenspotted lady beetle and multicolored Asian lady beetle were the third- and fourth-most abundant species, respectively. The seven most abundant species constituted 99% of all lady beetles sampled and were recorded from all six habitats. However, lady beetle species ranged considerably in their evenness of habitat use, resulting in differences in rank abundance among habitats. Lady beetle assemblages were similar for alfalfa and winter wheat, but not with other habitats, which possessed distinct lady beetle assemblages in rank abundance. Annual abundance of lady beetles varied considerably within habitats, but declining trends were evident from significant negative regressions in annual abundance for adult and immature lady beetles in corn and adults in soybean. As a group, native adult lady beetles showed a significant declining trend in corn but not in other habitats, whereas trends for non-native lady beetles were non-significant in all habitats. Sample rates of lady beetles in alfalfa, spring grains, and corn in this study were 71%, 25% and 6%, respectively, compared that of a previous study from the region, further indicating substantial decreases in lady beetle abundance. Possible explanations and implications for observed patterns in lady beetle diversity and individual species abundances in field crops and restored prairie of eastern South Dakota are discussed with respect to prey, agronomic trends, and landscape factors.

Technical Abstract: Lady (= ladybird) beetles provide agroecosystem services as major predators of aphids and other pests of field crops. Several native lady beetle species in North America have declined in association with the introduction of invasive species of lady beetles. In particular, populations of three native species declined drastically (Coccinella transversoguttata richardsoni) or effectively disappeared (Coccinella novemnotata, Adalia bipunctata) from agricultural landscapes in eastern South Dakota, U.S.A., following establishment of an invasive lady beetle (Coccinella septempunctata) in the 1980s. Since then, two other non-native lady beetles (Harmonia axyridis and Hippodamia variegata) have established in eastern South Dakota, but long-term analysis of their impact on the aphidophagous lady beetle guild is lacking. This paper summarizes long-term results from 14 years (2007-2020) of sampling lady beetles by sweepnet and timed searches in five field crops and restored prairie in eastern South Dakota. In all, 17,099 aphidophagous lady beetles comprising 10 species were sampled. Two invasive species (Coc. septempunctata, Har. axyridis) were the third- and fourth-most abundant species, respectively. The seven most abundant species constituted 99% of all coccinellids sampled and were recorded from all six habitats. However, coccinellid species ranged considerably in their evenness of habitat use, resulting in differences in rank abundance among habitats. Coccinellid assemblages were similar for alfalfa and winter wheat, but not with other habitats, which possessed distinct coccinellid assemblages in rank abundance. Annual abundance of lady beetles varied considerably within habitats, but declining trends were evident from significant negative regressions in annual abundance for adult and immature coccinellids in corn and adults in soybean. As a group, native adult coccinellids showed a significant declining trend in corn but not other habitats, whereas trends for non-native adult coccinellids were non-significant in all habitats. Sample rates of coccinellids in alfalfa, spring grains, and corn in this study were 71%, 25% and 6%, respectively, compared that of a previous study from the region, further indicating substantial decreases in coccinellid abundance. Possible explanations and implications for observed patterns in lady beetle diversity and individual species abundances in field crops and restored prairie of eastern South Dakota are discussed with respect to prey, agronomic trends and landscape factors.