BOB HIRSHON (host):
A butterfly’s medicine chest…I’m Bob Hirshon and this is Science Update.
Monarch butterflies feed on milkweed plants. And chemicals in the plants make the butterflies toxic to predators such as birds. Milkweed also protects the monarchs from harmful parasites, according to evolutionary biologist Jaap de Roode of Emory University. He says some milkweed species have more parasite-fighting chemicals than others, and he and his colleagues found that this affects where the butterflies lay their eggs.
JAAP DeROODE (Emory University):
Monarchs when they’re infected with this parasite, prefer to lay their eggs on plants that will make their offspring less sick.
But uninfected butterflies didn’t have a preference.
Why don’t all Monarchs choose these medicinal plants? I think it’s the same with humans when we take medication when we’re sick. Alot of medication has side effects, and so we don’t want to take it when we don’t need it.
I’m Bob Hirshon, for AAAS, the science society.