The Perception of Plant Allelochemicals That Inhibit Feeding

Plant-feeding insects have evolved an array of subtle discrimination capabilities involving their chemical senses. During the last 25 years an extensive list of plant chemicals that are detected by the contact and olfactory chemical senses of insects has accumulated. This list together with some 25–30 species of insects for which we have electrophysiological data on their chemical senses form the basis for our understanding of the chemical control of feeding. Many additional experiments at the behavioral level leave little doubt that the feeding of insects is regulated by some “umwelt” of plant chemicals, but the unique messages offered by host and nonhost plants have yet to be discovered (Dethier and Crnjar, 1982). The dynamic aspects of plant chemistry, as well as the many plant surface compounds that may have behavioral significance add to the complexity of this task (Fobes et al., 1985; Berenbaum, 1985; Gibson and Pickett, 1983; Woodhead, 1983). In addition, several types of physiological feedbacks that are important in regulating feeding have many details yet to be resolved (Shirahashi and Yano, 1984; Bernays and Simpson, 1982). These limitations in our understanding of the regulation of insect feeding come sharply into focus when we attempt to understand the importance of plant allelochemicals that inhibit feeding.