Palatability of Coloradia pandora (Lepidoptera: Saturniidae) Eggs to a Rodent Predator: Contributions of Physical and Chemical Characteristics

Abstract

Field observations of remnants from predation on pandora moths, Coloradia 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 enemy of C. pandora that rejects eggs while feeding on moths. Nutritional analyses indicated C. pandora moths (both females and males) and eggs are of comparable food quality, so additional feeding trials were conducted 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 residue of egg tissue. Whole eggs, whole shells, and ground shells did inhibit consumption by the same ground squirrels. A follow-up trial with a naive group of S. lateralis confirmed that whole eggs and whole shells inhibit consumption. Consumption of egg contents was equivalent to controls for both groups of S. lateralis. We conclude that C. pandora eggs are protected physically, but not chemically, from consumption by S. lateralis. The foraging range of S. lateralis, a generalist predator in central Oregon, includes the lower canopy of pine ( Pinus spp.) forests where C. pandora eggs are deposited. Therefore, the tough eggshell probably inhibits S. lateralis predation of C. pandora eggs under natural conditions.