Remarkably, the caterpillar develops a stronger taste for chemicals specifically found in plants that will cure its infection, according to Michael Singer, assistant professor of biology, who coauthored a paper in the July 28 issue of Nature with Elizabeth Bernays at the University of Arizona.
No one has ever observed a species that changes the behavior of its taste buds, known as its gustatory cells, in response to an infection, say the authors.
When the caterpillars are attacked by parasites common to southern Arizona, the fuzzy black and orange creatures start eating the threadleaf groundsel, a shrubby member of the sunflower family that contains parasite- killing chemical compounds called pyrrolizidine alkaloids, or PAs. These alkaloids can inflict fatal liver damage on a human, but the caterpillar is able to sequester the toxins in a harmless form in its blood, ready to revert to the toxic form if consumed by a parasite.
Singer and Bernays determined that receptors on the caterpillar’s taste buds fire much more rapidly in the presence of PAs when the caterpillar is infected compared to uninfected caterpillars.
Singer told the Hartford Courant, which published a page-one story about the research, that the caterpillar behavior is clearly not learned. “Even among insects, they are not that bright,” he said. “They are essentially a big gut. There is not a lot of room for brain power.”
Other animals, such as chimpanzees, are capable of learning that certain plants in their environments have medicinal value.