RESUMEN
We have developed and tested a technique to microencapsulate terpene compounds by forming gelatin-walled microcapsules around the terpene essential oils. Eight terpenes that are common constituents of Douglas fir (Pseudotsuga menziesii) oleoresin were encapsulated, including five monoterpenes (α-pinene,ß-pinene, camphene, myrcene, and limonene) and three oxygenated monoterpenes (bornyl acetate, linalool, andß-citronellol). The encapsulated terpenes were mixed into artificial diets to determine the effects they had on western spruce budworm (Choristoneura occidentalis) survival and reproduction, using a three-generation bioassay. We describe the technique and present data from preliminary bioassays with seven of the terpenes to demonstrate thatC. occidentalis larvae would consume diets fortified with microencapsulated terpenes. The technique is useful because it helps to reduce the rate at which terpenes volatilize from the diets and it "packages" the terpenes in a manner more closely resembling the way they are present in the resin canals of plant foliage. Many scientists investigating the biological importance of terpenes in mediating plant-herbivore interactions may find that microencapsulated terpenes are useful in both laboratory diet studies and field and greenhouse experiments with plant material.