Endemic populations of pandora moths (Co/oradia pandora Blake), a defoliator of western pine forests, proliferated to epidemic levels in central Oregon in 1986 and increased dramatically through 1 994. Golden-mantled ground squirrels (Spermophilus lateralis Say) consume adult pandora moths, but reject nutritionally valuable eggs from gravid females. Feeding trials with captive S. lateralis were conducted to identify the mode of egg protection. Chemical constituents of fertilized eggs were separated through a polarity gradient of solvent extractions. Consumption of the resulting hexane, dichloromethane, and water egg fractions, and the extracted egg tissue residue, was evaluated by randomized 2-choice feeding tests. Consumption of four physically distinct egg fractions (whole eggs, "whole" egg shells, ground egg shells, and egg contents) also was evaluated. These bioassays indicated that C. pandora eggs are not protected chemically, however, the egg shell does inhibit S. lateralis consumption. Egg protection is one mechanism that enables C. pandora to persist within the forest food web. Spermophilus lateralis, a common and often abundant rodent of central Oregon pine forests, is a natural enemy of C. pandora moths and pupae, but not eggs. / Graduation date: 1995