Terpenes as repellents

Until rather recently, our choice among chemicals repellant to insects was very limited (9), and some of the available remedies seem to have been almost equally repellent to their human users. The most familiar of them undoubtedly is the classical oil of citronella, a mixture of plant terpenes which consists principally of geraniol, citronellol, and citronellal. It is a remarkable coincidence that at least one insect species, an ant discussed by Dr. Happ, also makes use of some of these same terpenes as repellents against other insects. It biosynthesizes them de novo rather than simply taking them from plant sources. Many other examples of insect repellency have been observed (9), and Roth and Eisner (28) list over 30 compounds which have been identified as defense substances of anthropods. 

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