Monarch butterfly and milkweed declines substantially predate the use of genetically modified crops

Monarch butterfly (Danaus plexippus) decline over the past 25 years has received considerable public and scientific attention, in large part because its decline, and that of its milkweed (Asclepias spp.) host plant, have been linked to genetically modified (GM) crops and associated herbicide use. Here, we use museum and herbaria specimens to extend our knowledge of the dynamics of both monarchs and milkweeds in the United States to more than a century, from 1900 to 2016. We show that both monarchs and milkweeds increased during the early 20th century and that recent declines are actually part of a much longer-term decline in both monarchs and milkweed beginning around 1950. Herbicide-resistant crops, therefore, are clearly not the only culprit and, likely, not even the primary culprit: Not only did monarch and milkweed declines begin decades before GM crops were introduced, but other variables, particularly a decline in the number of farms, predict common milkweed trends more strongly o...

过去25年间，帝王蝶（Danaus plexippus）种群衰减引发了公众与学界的广泛关注，这在很大程度上源于其种群下降及其寄主植物马利筋属（Asclepias spp.）的数量锐减均与转基因（GM）作物及相关除草剂的使用存在关联。本研究借助博物馆馆藏标本与植物标本馆馆藏标本，将美国境内帝王蝶与马利筋种群动态的研究周期拓展至一个多世纪（1900年至2016年）。研究结果表明，20世纪早期帝王蝶与马利筋种群均呈现增长态势，而近期的种群衰减实则是两者自1950年左右开启的长期种群下降过程的一部分。由此可见，抗除草剂作物显然并非导致种群下降的唯一元凶，甚至可能并非主要元凶：不仅帝王蝶与马利筋的种群衰减早在转基因作物推广数十年前就已启动，其他变量——尤其是农场数量减少——对普通马利筋种群趋势的预测性更强（原文后续内容未完整给出）。