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Bloodflowers’ risk to monarchs could multiply as climate changes

Heat and CO2 scenarios suggest a milkweed species becomes toxic or useless to caterpillars

By
6:58pm, July 10, 2018
monarch butterfly on tropical milkweed

MONARCH BEWARE  As the climate changes, lovely tropical milkweed popular in gardens may become even more of a danger to monarch butterflies than it is now.

Climate change could make a showy invasive milkweed called a bloodflower even more of a menace for monarch butterflies than it already is.

Monarch caterpillars, which feed on plants in the milkweed family, readily feast on Asclepias curassavica. Gardeners in the southern United States plant it for its showy orange blooms, yet the species “is turning out to be a bit of a nightmare,” says Mark Hunter of the University of Michigan in Ann Arbor.

Monarchs (Danaus plexippus) migrating south to Mexico in the fall come across bloodflower bonanzas and don’t bother to keep on flying. Full migration normally prevents a harmful Ophryocistis parasite from building up in the insect population. Cutting the cycle short lets infection flourish.

In experiments, bloodflowers grown in outdoor enclosures under high carbon dioxide concentrations, around 760 parts

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