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The Mexican bean beetle, Epilachna varivestis Mulsant, feeds selectively on certain species of Phaseolus to the exclusion of the remaining representatives of this and other genera of beans. In a study of the chemical factors underlying this selective feeding, the phagostimulant fraction in the seeds of P. vulgaris was isolated and identified as sucrose. Bioassay of 13 sugars and 15 amino acids showed that only sucrose and, to a lesser degree, its hexose components induced feeding by the beetle. The seeds as well as leaves of the nonresistant species of Phaseolus were found to have a higher concentration of sucrose, glucose, and fructose, thereby revealing the role these sugars play as arrestants in hostplant selection by the beetle. Bioassay of the volatile

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