Japanese beetles' feeding on milkweed flowers may compromise efforts to restore monarch butterfly habitat
Baker AM, Potter DA. Scientific reports, August 2018.
Read the paper Free to read · doi:10.1038/s41598-018-30731-z
What this paper is about
Japanese beetles gather on common milkweed flowers and eat them. In the field they cut fruiting and seed set by more than 90 percent and wrecked the umbels.
Millions of milkweeds are being planted to replace what was lost from cropland. If an invasive beetle stops those plants setting seed, the restoration does not compound.
Summarised here from the abstract below. Not the authors’ words.
Abstract
The eastern North American migratory population of monarch butterflies (Danaus plexippus) is in serious decline. Habitat restoration, including adding millions of host plants to compensate for loss of milkweed in US cropland, is a key part of the international conservation strategy to return this iconic butterfly to sustainable status. We report here that Popillia japonica, a polyphagous, invasive beetle, aggregates and feeds on flowers of Asclepias syriaca, the monarch's most important larval food plant, reducing fruiting and seed set by >90% and extensively damaging milkweed umbels in the field. The beetle's ongoing incursion into the monarch's key breeding grounds in the US Midwest is likely to limit pollination and outcrossing of wild and planted milkweeds, reducing their capacity to colonize new areas via seeds. Popillia japonica represents a previously undocumented threat to milkweeds that should be considered in models for monarch habitat restoration.
Abstract reproduced from the published paper, which is licensed CC BY. Copyright remains with the authors.
Milkweeds in this paper
- Common Milkweed Asclepias syriaca
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Milkweed USA. (2026). Japanese beetles' feeding on milkweed flowers may compromise efforts to restore monarch butterfly habitat (listing). Retrieved DATE, from https://milkweedusa.com/research/japanese-beetles-feeding-on-milkweed-flowers-may-compromise-efforts-2018/
"Japanese beetles' feeding on milkweed flowers may compromise efforts to restore monarch butterfly habitat (listing)." Milkweed USA, 2026, https://milkweedusa.com/research/japanese-beetles-feeding-on-milkweed-flowers-may-compromise-efforts-2018/. Accessed DATE.
Milkweed USA. "Japanese beetles' feeding on milkweed flowers may compromise efforts to restore monarch butterfly habitat (listing)." Last modified 2026-08-01. Accessed DATE. https://milkweedusa.com/research/japanese-beetles-feeding-on-milkweed-flowers-may-compromise-efforts-2018/.
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title = {Japanese beetles' feeding on milkweed flowers may compromise efforts to restore monarch butterfly habitat (listing)},
author = {{Milkweed USA}},
year = {2026},
url = {https://milkweedusa.com/research/japanese-beetles-feeding-on-milkweed-flowers-may-compromise-efforts-2018/},
note = {Accessed DATE}
}