The Role of Monoterpenes from California Bay in Nest Ectoparasite Control by Dusky-Footed Wood Rats

Anna Payne-Tobin, Vassar College ’08, Prof. Richard B. Hemmes and Edith C. Stout

Nest-borne ectoparasites can exact serious fitness costs to hosts both directly through blood removal and as vectors of microbial disease. Several species of birds appear to integrate fresh foliage from aromatic plants into their nests to reduce the abundance of such parasites. So far, the dusky-footed wood rat (Neotoma fuscipes) appears to be the only mammal for which evidence of nest fumigation behavior is reasonably compelling. This rat brings into its stickhouse a diversity of foliage types, some of which serve as food but others like California bay (Umbellularia californica) which it selectively places near its sleeping nest contain volatile oils with biocidal properties and may serve as a nest fumigant. Our current work seeks to establish 1) which monoterpenes found in bay singly or in combination have the greatest potential to control nest fleas, 2) whether levels of monoterpenes in stickhouses are higher than in ambient air and 3) whether there is an association between bay foliage near the nest and abundance of ectoparasites in the nest.

The monoterpene content of California bay was characterized using gas chromatograph mass spectrometry (GC-MS). Monoterpenes were then tested for insecticidal properties in bioassays using fleas (Ctenocephalides felis). Umbellulone, the most abundant monoterpene constituent of bay, is not commercially available, so we extracted it from bay foliage by high performance liquid chromatography. In the field, we placed activated charcoal strips in the stickhouses near the nests to capture volatiles. The strips were analyzed by GC-MS and the results compared with occurrence of green plants and the ectoparasite counts from their respective nests. Monoterpenes from bay, including umbellulone, were found on the charcoal strips, indicating that the monoterpenes were volatile enough to contribute to the chemical environment of the sleeping nest.