Table_3_Declining Abundance of Coccinellidae (Coleoptera) Among Crop and Prairie Habitats of Eastern South Dakota, USA.docx

Lady (= ladybird) beetles (Coleoptera: Coccinellidae) provide agroecosystem services as major predators of aphids and other pests of field crops. Several native coccinellids 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 coccinellid (Coccinella septempunctata) in the 1980s. Since then, two other non-native coccinellids (Harmonia axyridis and Hippodamia variegata) have established in eastern South Dakota, but long-term analysis of their impact on the aphidophagous coccinellid guild is lacking. This paper summarizes long-term results from 14 years (2007–2020) of sampling coccinellids by sweepnet and timed searches in five field crops and restored prairie in eastern South Dakota. In all, 17,338 aphidophagous coccinellids 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 for other habitats, which possessed distinct coccinellid assemblages based on rank abundance. Annual abundance of coccinellids 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 in 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 74, 26, and 6%, respectively, compared to that of a previous study from the region, further indicating substantial decreases in coccinellid abundance. Possible explanations and implications for observed patterns in coccinellid 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.

瓢虫（ladybird beetle，鞘翅目Coleoptera、瓢虫科Coccinellidae）作为蚜虫及大田作物其他害虫的主要捕食者，可为农业生态系统提供关键生态服务。北美本土的多种瓢虫已随着入侵性瓢虫物种的引入而出现种群衰退。具体而言，自20世纪80年代入侵性瓢虫七星瓢虫（Coccinella septempunctata）在南达科他州东部农业景观定殖后，当地3种本土瓢虫的种群发生了显著变化：横纹瓢虫（Coccinella transversoguttata richardsoni）种群大幅锐减，九斑瓢虫（Coccinella novemnotata）与二斑瓢虫（Adalia bipunctata）则几乎完全消失。自此之后，另外两种非本土瓢虫——异色瓢虫（Harmonia axyridis）与多异瓢虫（Hippodamia variegata）——也在该区域定殖，但目前仍缺乏针对其对食蚜瓢虫类群（aphidophagous coccinellid guild）影响的长期分析研究。本研究总结了2007至2020年共14年间，在南达科他州东部5种大田作物与恢复草原（restored prairie）中，通过扫网法（sweepnet）与定时搜索法（timed searches）开展的瓢虫采样长期结果。本次采样共收集到10种食蚜瓢虫，总计17338头。两种入侵性瓢虫（七星瓢虫Coccinella septempunctata、异色瓢虫Harmonia axyridis）分别为第三、第四优势物种。种群丰度排名前七的瓢虫物种占总采样个体数的99%，且在全部6类生境中均有分布。但不同瓢虫物种的生境利用均匀度差异显著，进而导致各生境中的物种丰度排名存在明显差异。苜蓿与冬小麦生境中的瓢虫群落组成相似，但其余生境则各具独特的物种丰度排序结构，群落组成差异显著。各生境中瓢虫的年丰度波动幅度较大，但玉米生境中成虫与幼虫的年丰度均呈显著负回归趋势，大豆生境中成虫的年丰度亦呈现下降趋势。整体而言，本土瓢虫成虫仅在玉米生境中呈显著下降趋势，其余生境未表现出该特征；而非本土瓢虫成虫在所有生境中的种群趋势均无显著性。相较于该区域此前的研究，本研究中苜蓿、春谷类作物与玉米生境中的瓢虫采样率分别为74%、26%与6%，进一步印证了瓢虫种群丰度已出现大幅下降。本文针对南达科他州东部大田作物与恢复草原中观测到的瓢虫多样性及单物种种群丰度格局，结合猎物资源、农艺趋势与景观因子，探讨了其可能的成因与研究意义。