Exposure to Non-Native Tropical Milkweed Promotes Reproductive Development in Migratory Monarch Butterflies
Majewska AA, Altizer S. Insects, August 2019.
Read the paper Free to read · doi:10.3390/insects10080253
What this paper is about
Tropical milkweed planted along the southern coast does not die back in winter, and monarchs at those sites breed year-round instead of migrating.
This study tested whether exposure to the plant itself interferes with reproductive diapause, the hormonal state that holds off breeding. Monarchs exposed to it developed reproductively when they should have been pausing.
Summarised here from the abstract below. Not the authors’ words.
Abstract
BackgroundNorth American monarchs (Danaus plexippus) are well-known for their long-distance migrations; however, some monarchs within the migratory range have adopted a resident lifestyle and breed year-round at sites where tropical milkweed (Asclepias curassavica) is planted in the southern coastal United States. An important question is whether exposure to exotic milkweed alters monarch migratory physiology, particularly the ability to enter and remain in the hormonally-induced state of reproductive diapause, whereby adults delay reproductive maturity. Cued by cooler temperatures and shorter photoperiods, diapause is a component of the monarch's migratory syndrome that includes directional flight behavior, lipid accumulation, and the exceptional longevity of the migratory generation.MethodsHere, we experimentally test how exposure to tropical milkweed during the larval and adult stages influences monarch reproductive status during fall migration. Caterpillars reared under fall-like conditions were fed tropical versus native milkweed diets, and wild adult migrants were placed in outdoor flight cages with tropical milkweed, native milkweed, or no milkweed.ResultsWe found that monarchs exposed to tropical milkweed as larvae were more likely to be reproductively active (exhibit mating behavior in males and develop mature eggs in females) compared to monarchs exposed to native milkweed. Among wild-caught fall migrants, females exposed to tropical milkweed showed greater egg development than females exposed to native or no milkweed, although a similar response was not observed for males.ConclusionsOur study provides evidence that exposure to tropical milkweed can increase monarch reproductive activity, which could promote continued residency at year-round breeding sites and decrease monarch migratory propensity.
Abstract reproduced from the published paper, which is licensed CC BY. Copyright remains with the authors.
Key terms
Milkweeds in this paper
- Tropical Milkweed Asclepias curassavica
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"Exposure to Non-Native Tropical Milkweed Promotes Reproductive Development in Migratory Monarch Butterflies (listing)." Milkweed USA, 2026, https://milkweedusa.com/research/exposure-to-non-native-tropical-milkweed-promotes-reproductive-development-2019/. Accessed DATE.
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title = {Exposure to Non-Native Tropical Milkweed Promotes Reproductive Development in Migratory Monarch Butterflies (listing)},
author = {{Milkweed USA}},
year = {2026},
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