INFLUENCE OF SAGEBRUSH TERPENOIDS ON MULE DEER PREFERENCE

The effect on mule deer (Odocoileus hemionus hemionus Rafinesque) preference of compounds in mountain big sagebrush [Artemisia tridentata Nutt. ssp. vaseyana (Rydb.) Beetle], Wyoming big sagebrush (A.t. ssp. wyomingensis Beetle and Young), basin big sagebrush (A.t. ssp. tridentata), and black sagebrush (A. nova Nels.) was compared using a two-choice preference test. Compounds tested included: p-cymene, 1,8-cineole, methacrolein (two concentrations), and the nonvolatile crude terpenoid fraction (NVCTF) from each taxon. The compounds were tested by applying them to chopped alfalfa hay at concentrations similar to those found in nature. The intake of the treated hay was compared with that of an untreated control. Eight deer were used as test animals in an 8 x 8 Latin-square design. All compounds tested significantly deterred ingestion (P < 0.05). Compound influence on preference, in order of increasing deterrence, was as follows: 50% methacrolein, mountain big sagebrush NVCTF, methacrolein, basin big sagebrush NVCTF, p-cymene, Wyoming big sagebrush NVCTF, black sagebrush NVCTF, and 1,8-cineole. Methacrolein appears to be an important preference determinant among big sagebrush subspecies, and p-cymene between black sagebrush and big sagebrush. The NVCTFs containing sesquiterpene lactones as one of their constituents were closely related to the preference of all four taxa. Future studies of animal preference for sagebrush should consider all of the potential defensive chemicals in the foliage.