Air Date: Week of May 17, 2002

Living on Earth’s Maggie Villiger reports on a novel survival technique for a caterpillar -- producing its own insecticide.

Transcript

CURWOOD: Just ahead, some folks love them and others hate them. A California town battles over exotic eucalyptus trees. First, this Animal Note from Maggie Villiger.

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VILLIGER: The European cabbage butterfly is considered a pest here in North America where it likes to feast on vegetables like cauliflower, Brussels sprouts, and of course, cabbage. Scientists wondered what allows this species to gain such a strong foothold wherever it goes. The bug’s secret turns out to be a chemical defense system it produces in its larval stage. Rows of hairs run along the length of these caterpillars’ bodies. The tips of these hairs secrete a clear, oily fluid that collects in drops. In laboratory experiments, researchers watched as ants interacted with the cabbage butterfly caterpillars. As soon as an ant touched the caterpillar’s glistening hairs, it would back off and start frantically cleaning whichever body part had even brushed against the larva.

Caterpillars of the European cabbage butterfly, Peris rapae, (top image) are beset with glandular hairs, bearing droplets of a clear, oily secretion at their tips (image 2A). The tip of each hair is elaborately sculpted (images 2B & C), perhaps allowing the secretion to be held in place as the droplets build up. Ants keep their distance from the caterpillars, and spend a significant amount of time cleansing themselves after making contact with the caterpillar and its offensive secretions (images 2D, E & F).

For good measure, the ant would also clean the body part it had used to clean the initial point of contact. When the scientists isolated the irritating secretion they found a new group of chemicals they named mayolenes. These chemicals derive from a family of compounds that plants use to repel insect attacks. It looks like the European cabbage butterfly is such a successful invader thanks to its own shield of insect repellant. That’s this week’s Animal Note. I’m Maggie Villiger.

[THEME MUSIC OUT]

CURWOOD: And you’re listening to Living on Earth.

[MUSIC: Mellanova, "???," KNOW YOUR ENEMY (Archenemy – 2000)]