Many higher plants produce economically important organic compounds such as oils, resins, tannins, natural rubber, gums, waxes, dyes, flavors and fragrances, pharmaceuticals, and pesticides. However, most species of higher plants have never been described, much less surveyed for chemical or biologically active constituents, and new sources of commercially valuable materials remain to be discovered. Advances in biotechnology, particularly methods for culturing plant cells and tissues, should provide new means for the commercial processing of even rare plants and the chemicals they produce. These new technologies will extend and enhance the usefulness of plants as renewable resources of valuable chemicals. In the future, biologically active plant-derived chemicals can be expected to play an increasingly significant role in the commercial development of new products for regulating plant growth and for insect and weed control.

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The mosquito feeding and ovipositional repellency of the major monoterpenoid present in the volatile oil ofHemizonia fitchii (Asteraceae), i.e., 1,8-cineole, was investigated. Although 1,8-cineole did not exhibit any significant mosquito larvicidal activity, it was moderately effective as a feeding repellent and highly effective as an ovipositional repellent against adultAedes aegypti (yellow fever mosquito). The ovipositional repellency of 1,8-cineole, coupled with the presence of severalHemizonia chromenes previously shown to possess mosquito larvicidal activity, may therefore account in large part for the observed suppression of local mosquito populations which was associated withH. fitchii plants in northern California.

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