Moths Remember Caterpillar Life

March 6, 2008 -- During the dramatic transformation from caterpillar to moth, memories and minds remain at least somewhat intact, according to a new study.

Published in this week's PLoS ONE, the study found that moths and perhaps butterflies often recall what they learn as ground-dwelling insects, revealing how resilient memory may be.

"Caterpillars are built for crawling and chewing plant material, while moths and butterflies are built for flying and drinking nectar," explained Douglas Blackiston, who led the recent study. "As such, the adult butterfly must rearrange its digestive system and develop distinct muscles for flight and walking on its long legs."

The morphing caterpillar's brain also grows in size and complexity to reflect the insect's drastic lifestyle transition. Whether its memories endure during those changes was a mystery, until now.

To test more specifically what goes on in the insect's mind during metamorphosis, Blackiston and his colleagues borrowed tobacco hornworm caterpillar larvae from the North Carolina State University Insectary in Raleigh, N.C. The researchers conditioned the caterpillars to avoid the chemical ethyl acetate, which smells like pear juice.

Blackiston conducted the research in the labs of developmental biologist Elena Casey and behavioral ecologist Martha Weiss at Georgetown University in Washington, D.C.

Since caterpillars don't naturally avoid ethyl acetate, the researchers gave some of the insects a mild electrical shock whenever they encountered it. The insects quickly learned to avoid the telltale odor.

After the caterpillars morphed into moths, the scientists exposed them to the chemical again.