PALATABILITY OF COLORADIA-PANDORA (LEPIDOPTERA, SATURNIIDAE) EGGS TO A RODENT PREDATOR - CONTRIBUTIONS OF PHYSICAL AND CHEMICAL CHARACTERISTICS

Field observations of remnants from predation on pandora moths, Colora dia pandora Blake, suggested that eggs from gravid females were being rejected. Captive feeding trials with golden-mantled ground squirrels, Spermophilus lateralis Say, verified that this rodent is a natural en emy of C, pandora that rejects eggs while feeding on moths. Nutritiona l analyses indicated C. pandora moths (both females and males) and egg s are of comparable food quality, so additional feeding trials were co nducted to determine why eggs were unpalatable to the ground squirrels . Chemical fractions of eggs did not inhibit consumption consistently enough to explain the rejection behavior; neither did the extracted re sidue of egg tissue. Whole eggs, whole shells, and ground shells did i nhibit consumption by the same ground squirrels. A follow-up trial wit h a naive group of S. lateralis confirmed that whole eggs and whole sh ells inhibit consumption. Consumption of egg contents was equivalent t o controls for both groups of S. lateralis. We conclude that C. pandor a eggs are protected physically, but not chemically, from consumption by S. lateralis. The foraging range of S. lateralis, a generalist pred ator in central Oregon, includes the lower canopy of pine (Pinus spp.) forests where C. pandora eggs are deposited. Therefore, the tough egg shell probably inhibits S. lateralis predation of C. pandora eggs unde r natural conditions.