Researchers investigated how changing temperatures affect monarch butterflies and their parasite, Ophryocystis elektroscirrha. Infections with this parasite have more than tripled since 2002. The new field study exposed both infected and uninfected monarchs to fluctuating ambient or elevated temperatures while they fed on either nonnative tropical milkweed or native swamp milkweed. The study found monarchs in warmer conditions were 22% less tolerant of infection.
Earlier laboratory experiments had used constant high temperatures and suggested parasites might not survive extreme heat, and that higher plant toxin levels could help butterflies. In contrast, the field experiment showed that under hotter, realistic temperature cycles the expected protection from tropical milkweed largely disappeared. Most exposed butterflies became infected, and parasites performed better than researchers anticipated.
The team observed that tropical milkweed toxins rose slightly with warmth. Very strong toxins can slow caterpillar development and damage cells; sometimes monarchs excrete those toxins and lose protection. Lead author Sonia Altizer notes that warmer temperatures can reduce the plants' medicinal effect and may make a warmer world "a sicker world for monarchs." The study appears in Ecological Entomology and was led by Isabella Ragonese and Christopher Brandon. Source: University of Georgia.
Difficult words
- parasite — organism that lives on and harms another
- fluctuate — change up and down over timefluctuating
- ambient — surrounding environmental temperature or conditions
- tolerant — able to withstand infection or stress
- milkweed — a plant that monarch caterpillars eattropical milkweed, swamp milkweed
- toxin — a poisonous chemical produced by plants or animalstoxins
- medicinal — having effects that can treat or prevent disease
- excrete — eliminate waste or unwanted substances from body
Tip: hover, focus or tap highlighted words in the article to see quick definitions while you read or listen.
Discussion questions
- How might a reduced medicinal effect of milkweed affect monarch survival in warmer climates?
- Should conservation efforts promote native swamp milkweed over nonnative tropical milkweed? Why or why not, based on the study?
- What further studies would help clarify how realistic temperature cycles affect parasites and monarchs?
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