alpha-Ionone, alpha-ionol, and their mixtures with phenolic volatiles act as potential male lures for the solanaceous fruit fly Bactrocera latifrons (Hendel). However, the attractiveness of these compounds is not as strong as that of other well-known tephritid male lures, such as methyl eugenol for Bactrocera dorsalis. Isophorone and isophorol, which have a partial skeletal structure of alpha-ionone/alpha-ionol (i.e., trimethylcyclohexene), were attractive to B. latifrons males, and their mixtures with alpha-ionol exhibited stronger activity than any of the individual compounds. We also tested 3-oxo-alpha-ionone, 3-oxo-alpha-ionol, 3-hydroxy-alpha-ionone, and 3-hydroxy-alpha-ionol, hybrid compounds between isophorone/isophorol and alpha-ionone/alpha-ionol. 3-Oxo-alpha-ionone and 3-oxo-alpha-ionol were active both as attractants and phagostimulants for males. The results suggest that the introduction of an oxygen atom at the 3-position of the alpha-ionone/alpha-ionol molecule optimizes the specific chemosensory responses in B. latifrons males.
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.
A series of 3-oxygenated derivatives of a-ionone and a-ionol have been characterized as highly specific male lures for the solanaceous fruit fly Bactrocera latifrons (Hendel). In order to optimize the activity, we tested several analogous compounds derived from the three known attractants, 3-oxo-a-ionone, 3-oxo-a-ionol, and 3-hydroxy-a-ionone. 3-Oxo-7,8-dihydro-a-ionone and 3-oxo-7,8-dihydro-a-ionol were found to be potent attractants as well as feeding stimulants for the males in an indoor bioassay. While trans-3-hydroxy-a-ionone showed moderate attractant and feeding stimulant activity, the corresponding cis-isomer was weakly active, indicating the importance of the stereochemistry at the C-3 position. Synthetic trans-3-acetoxy-a-ionone exhibited lower activity than the corresponding 3-hydroxy derivative. B. latifrons males fed actively on 3-oxo-7,8-dihydro-a-ionone, transformed it to 3-oxo-7,8-dihydro-a-ionol, and sequestered this compound in a substantial quantity in the rectal glands. Males that fed on 3-oxo-7,8-dihydro-aionol incorporated the compound mostly unchanged in the rectal gland. In both cases, the rectal content was approximately 1 mg/gland at 6 h post-feeding on the chemicals, respectively. Selective accumulation of these 3-oxygenated aionone/a-ionol analogs suggests their possible role as a male sex pheromone.
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