Monoterpene effect on feeding choice by deer

Area of Science:

• Ecology
• Zoology
• Plant Chemistry

Background:

• Sitka black-tailed deer (Odocoileus hemionus sitkensis) consumption of western redcedar (Thuja plicata) is inversely related to monoterpene levels.
• Monoterpenes are volatile organic compounds found in many plants, potentially influencing herbivore interactions.

Purpose of the Study:

• To investigate if monoterpenes in western redcedar act as feeding deterrents for Sitka black-tailed deer.
• To determine if this deterrent effect is species-specific by testing European roe deer (Capreolus capreolus) and rusa deer (Cervus timorensis russa).

Main Methods:

• Feeding choice experiments were conducted using solutions of five monoterpenes (sabinene, myrcene, alpha-pinene, d + l-limonene, and alpha,beta-thujone) at their highest natural concentrations.
• Experiments were performed on Sitka black-tailed deer, roe deer, and rusa deer to assess species-specific responses.
• Concentration-dependent effects of both hydrocarbon and oxygenated monoterpenes were analyzed.

Main Results:

• All tested monoterpenes demonstrated repellent effects across all deer species.
• Alpha,beta-thujone, a major monoterpene in redcedar foliage, exhibited the strongest repellent activity.
• Repellency of hydrocarbon monoterpenes increased with concentration, while alpha,beta-thujone remained strongly repellent even at lower concentrations.

Conclusions:

• Monoterpenes, particularly alpha,beta-thujone, serve as significant feeding deterrents for multiple deer species.
• The findings raise questions about the physiological mechanisms deer employ to cope with consuming monoterpene-rich plants.