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Terpenes, volatile plant secondary compounds produced by woody plants, have historically been thought to act as feeding deterrents for mammalian herbivores. However, three species of woodrats, Neotoma stephensi, N. lepida, and N. albigula, regularly consume juniper, which is high in terpenes, and N. stephensi and N. lepida are considered juniper specialists. By investigating the terpene profiles in Juniperus monosperma and J. osteosperma, which are browsed or avoided by woodrats in the field, and recording the caching and consumption of juniper foliage by woodrats in the lab, we have evidence that terpenes may serve as feeding and/or foraging cues. The obligate specialist N. stephensi chose to forage on trees higher in p-cymene and preferred to consume juniper rather than caching it in a laboratory setting. These observations provide evidence that terpenes serve as a feeding cue and that the obligate specialist's physiological mechanism for metabolizing the terpenes present in juniper may negate the need for caching. The facultative specialist N. lepida chose to forage on trees lower in four terpenes and cached more juniper than the obligate specialist N. stephensi, providing evidence that terpenes serve as a feeding deterrent for N. lepida and that this woodrat species relies on behavioral mechanisms to minimize terpene intake. The generalist N. albigula foraged on trees with higher terpenes levels but consumed the least amount of juniper in the lab and preferred to cache juniper rather than consume it, evidence that terpenes act as foraging but not feeding cues in the generalist. Our findings suggest that volatile plant secondary compounds can act as feeding and/or foraging cues and not just feeding deterrents in mammalian herbivores.

This study is a quantitative examination of primate feeding selectivity in relation to secondary chemistry within a single plant species, Hymenaea courbaril. It provides the first evidence that sesquiterpenes may act as feeding deterrents in mantled howler monkeys. A free-ranging group of mantled howler monkeys at the study site of Sector Santa Rosa, Area de Conservacion Guanacaste, Costa Rica were observed for the 2-month period of H. courbaril leaf flush in 1999. Tree characteristic data and leaf specimens were collected from 22 focal trees. Gas chromatography and mass spectrometry were used to estimate relative percentages of sesquiterpenes in leaf specimens. The monkeys fed only on the youngest leaves and only from particular trees. Whereas leaf stage selectivity was likely governed by tannin content and structural carbohydrates in younger and older leaf stages, respectively, differential tree use may be related to variability in sesquiterpene content. There is evidence that alpha-copaene may have played a role in interindividual tree use, and that cyperene may also be implicated. However, there is no reported evidence of antiherbivore activity for cyperene.

Based on field observations of the effects of the resinous tarweedHemizonia fitchii A. Gray (Asteraceae) on mosquito populations in California, the volatile oil of this plant was investigated for insecticidal activity. Analysis of thé oil by TLC and capillary GC-MS showed the presence of five major constituentś which were identified as the monoterpenoid 1,8-cineole, and the chromenes encecalin, eupatoriochromene (desmethylencecalin), 6-vinyl-7-methoxy-2,2-dimethylchromene, and desmethoxyencecalin. Trace amounts of several volatile fatty acids, alkanes,p-coumarate derivatives, additional chromene derivatives, and numerous mono- and sesquiterpenoids were also detected and identified by GC-MS. Fractionation of the oil by preparative TLC and column chromatography afforded the major chromenes, the identities of which were confirmed by NMR and IR spectral data. The chromenes exhibited weak to moderate toxicity againstCulex pipiens (house mosquito) larvae andOncopeltus fasciatus (large milkweed bug) nymphs. However, no antijuvenile hormone activity was observed for any of the compounds tested against these insect species.