Phloridzin, a plant-derived compound toxic to Rhagoletis pomonella (Walsh), the apple maggot fly, was degraded and detoxified by the bacterium Enterobacter agglomerans. Spectrophotometric and thin-layer chromatography data showed that E. agglomerans begins to use the glycoside in aqueous solution after 6 h of incubation at 24°C. All apple maggot flies that fed on three different concentrations of sterilized phloridzin solutions died within 24 h. Incubation of E. agglomerans in 0.001 and 0.01 M aqueous phloridzin for 3 d eliminated toxicity for apple maggot flies but most died after being fed a 1 M solution. Plant leachate containing phenolic compounds extracted from McIntosh apple leaves also was used by E. agglomerans. Enterobacter agglomerans entered logarithmic growth more quickly in leachate samples than in solutions of commercially-purified phloridzin. Protein, amino acid, and reducing sugar content of the leachate increased after incubation with E. agglomerans for 12 h. Reducing sugar content decreased, however, after 24 h of incubation, whereas protein and amino acid content continued to increase. Scanning electron micrographs of leachate intact on apple leaf surfaces revealed the presence of healthy rod-shaped bacteria and yeast aggregating about it. These images suggest that phylloplane microorganisms use leachate as a source of nutrients and this activity may affect the potency of plant defensive chemicals. The potential benefits afforded by the catabolic activities of phylloplane and/or gut microorganisms on plant compounds to apple maggot flies are discussed.