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‐α‐ionone. Sexually mature males that fed on the eggplant pulp selectively accumulated a series of 3‐oxygenated α‐ionone/α‐ionol analogs (e.g., 3‐oxo‐α‐ionol and 3‐oxo‐7,8‐dihydro‐α‐ionol) in the rectal gland, a suspected pheromone reservoir in male flies. Males fed on synthetic 3‐hydroxy‐α‐ionone, 3‐oxo‐α‐ionol, or 3‐oxo‐α‐ionone partially biotransformed the compounds into 3‐oxo‐α‐ionol, 3‐oxo‐α‐ionone, and 3‐oxo‐7,8‐dihydro‐α‐ionol and sequestered substantial quantities (as high as 5 µg/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.