Sequestration of 3-oxygenated α-ionone derivatives in the male rectal gland of the solanaceous fruit fly, Bactrocera latifrons

The solanaceous fruit fly, Bactrocera latifrons (Hendel) (Diptera: Tephritidae), infests various solanaceous fruits including eggplant and chili peppers. We found that a freshly cut fruit of an eggplant cultivar [Solanum melongena L. cv. Long Purple Oriental (Solanaceae)] selectively attracted and provoked voracious feeding behavior in adult B. latifrons males (but not in females) in an indoor test. One of the male-specific attractants/feeding stimulants in eggplant was identified as 3-hydroxy-alpha-ionone. Sexually mature males that fed on the eggplant pulp selectively accumulated a series of 3-oxygenated alpha-ionone/alpha-ionol analogs (e.g., 3-oxo-alpha-ionol and 3-oxo-7,8-dihydro-alpha-ionol) in the rectal gland, a suspected pheromone reservoir in male flies. Males fed on synthetic 3-hydroxy-alpha-ionone, 3-oxo-alpha-ionol, or 3-oxo-alpha-ionone partially biotransformed the compounds into 3-oxo-alpha-ionol, 3-oxo-alpha-ionone, and 3-oxo-7,8-dihydro-alpha-ionol and sequestered substantial quantities (as high as 5 mu g/gland as a mixture) in a similar ratio in the rectal gland within 6 h after ingestion. These results suggest that the rectal sequestrates may serve as a sex pheromone similar to other Bactrocera species that use phenylpropanoid volatiles to attract conspecific females.