CATERPILLAR OF THE WEEK: I have an ulterior motive for appointing the Luna Moth caterpillar (Actias luna) this week’s Caterpillar of the Week, which will be revealed in an upcoming spotlight on caterpillar anatomy. Spoiler alert: that post will involve prolegs—and you should definitely get excited! Anyway, we hardly need a reason to feature Lunas. Regarded by many as the most gorgeous insect in all of North America, they bring publicity to our lab, not the other way around!
There’s nothing quite like watching a vibrant green, wild Luna caterpillar chowing down on a leaf. During my first summer with the Lab in 2014, at a certain point, we hatched way too many locally collected Luna eggs. I had the privilege of releasing some early instars on hickory trees in my yard. Every day, I checked on them. Naturally, most disappeared due to predation, but a few reached their final instar, growing into a plump, juicy, luminous green body that we can never quite replicate in captivity. The experience was enthralling.
According to a 1989 study by Richard Lindroth, Luna caterpillars’ ability to eat those hickory leaves (as well as the leaves of many other preferred host plant species, such as butternut and walnut) depends on the Lunas’ enzyme production. Hickory, butternut, and walnut trees all produce a defensive chemical called juglone. Juglone can repel other plants from growing in the vicinity of these trees, and inhibit insects from dining on them.
Caterpillars reared on juglone-producing plants in Lindroth’s study developed highly increased levels of an enzyme that helped them tolerate juglone in their diets. Luna caterpillars reared on birch, which doesn’t produce juglone, had such low levels of this enzyme that Lindroth speculated their bodies never began to produce the enzyme at all.
Luna caterpillars have incredibly variable diets overall, but very specific local preferences. In Lindroth’s study, he attempted to raise Lunas on 11 different recorded host plants, and only experienced success with four of these. Why didn’t all of the caterpillars thrive? Lindroth hypothesized that local populations of Lunas are specifically adapted to certain host plant species, possibly based on the types of enzymes their bodies produce to help them consume their food. Since his Lunas all came from one regional population, they might not have been equipped with the adaptations necessary to eat plants that Lunas in other areas thrive on.
Stay tuned as Luna-palooza continues this week!
-Liz Kautz, TCL Education Director
"Caterpillar of the Week" will highlight a different species we grow in The Caterpillar Lab each week… or, you know, at least SOME weeks. We hope you enjoy meeting the caterpillars of New England!
More information on the Luna Moth on BugGuide here: http://bugguide.net/node/view/562
If you’d like to see a gorgeous and thorough account of one woman’s experience raising Lunas, check out this post we’ve been admiring on the Prairie Haven blog: http://www.aprairiehaven.com/?page_id=8543