Food Plant Use by Larvae of Milkweed Tiger Moth, Euchetes Egle (Drury)

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Kryger, Andrea
caterpillars; cocoons
thesis / dissertation description
Larvae of the milkweed tiger moth, Euchaetes egle, are specialist herbivores of the common milkweed, Asclepias syriaca. This highly modular host plant produces steroidal chemical defenses and E. egle is thought to be an aposematic insects that sequesters these defenses for use in its own defenses against natural enemies. Although this arctiid moth herbivore is common and widely distributed in North America, almost nothing is known about patterns of larval host plant use. The author tested the hypothesis that E. Egle is selective and collected data on the distribution of egg masses on leaves of A. syriaca left by ovipositing females in the field and data on the distribution and abundance of larvae on ramets of A. syriaca in south west Michigan. Using HPLC of leaves with and without larvae, the author found no evidence that steroidal cardenolides differed among leaves and could not detect cardenolides in the leaves sampled. In addition, E. egle showed no preference for the height of the plant, nor the height, width, or length of the leaf that the egg was laid on, but they did show a preference for laying their eggs on the bottom-side of the leaf, typically in the middle section. The author's results indicate that E. egle is found on leaves with no cardenolide chemical defenses, but this result was surprising and more research in this area is needed. Despite the conspicuous appearance of the later instar larvae of E. egle, which suggests aposematism, the larvae moved off ramets of A. syriaca during the day and fed more extensively at night.