Submitted to: Medical and Veterinary Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/2005
Publication Date: 12/1/2005
Citation: Carlson, D.A., Mramba, F., Sutton, B.D., Bernier, U.R., Geden, C.J., Mori, K. 2005. Sex pheromone of the tsetse fly, glossina austeni (diptera: glossinidae): isolation, identification of natural hydrocarbons and bioassay of synthesized compounds. Medical and Veterinary Entomology. 19:470-479. Interpretive Summary: Tsetse flies are vectors of a debilitating and fatal disease called Nagana in African cattle, and its variant, long known in humans as sleeping sickness. Scientists at the USDA, ARS, Center for Medical, Agricultural, and Veterinary Entomology laboratory in Gainesville, Florida were asked by the International Atomic Energy Agency to assist a visiting African scientist to find the sex pheromone in a species from East Africa, Glossina austeni. Natural compounds extracted from females were separated using a technique called gas chromatography. These chemicals were tested in Africa using male flies against treated decoys to find the most biologically active compounds, which turned out to be two unsaturated hydrocarbons. These were identified using mass spectrometry as 13,17-dimethyltritriacont-1-ene and 13,17-dimethylpentatriacont-1-ene after the samples had been reacted with dimethyldisulfide and deuterium. These highly stimulating compounds were also found in wild flies to show that they were consistently present in this species in nature. Corresponding synthetic compounds were then designed, obtained, and tested. The most biological activity was found in one optically active isomer, S,R-13,17-dimethyltritriacont-1-ene. It was active at 5 millionths of a gram and is the first sexual pheromone in a tsetse fly that is unsaturated. This information will be used to test factory-reared tsetse flies in large-scale rearing programs to ensure that wild flies and laboratory flies are compatible in large-scale sterile-male eradication programs.
Technical Abstract: Copulatory responses of male Glossina austeni (Newstead) (Diptera: Glossinidae), obtained in tests with frozen female flies, were not observed after solvent washing of cuticular lipids. Chromatographic analysis of extracts from laboratory-reared and field-collected G. austeni females yielded natural hydrocarbons that were highly stimulatory to males. Most of this activity was produced by compounds in the alkene fraction. Gas chromatograms (GC) contained five natural alkenes; these were separated by preparative GC for bioassays conducted in Tanzania. The two major alkenes were identified using GC-mass spectrometry (GC-MS) to be 13,17-dimethyltritriacont-1-ene and 13,17-dimethylpentatriacont-1-ene, after the samples had undergone derivatization using dimethyldisulfide and saturation with deuterium. These alkenes and natural alkanes were quantified from G. austeni of both sexes from laboratory and field samples to confirm that their presence was consistent in this species. Trials of synthetic samples resulted in the order of biological activity for the stereoisomers of 13,17-dimethyltritriacont-1-ene as follows: S,R-33:1 > R,S-33:1 > S,S-33:1 > R,R-33:1. Dose-response data showed an ED50 at 5 'g per treated, solvent-washed male decoy. Of the four stereoisomers of 13,17-dimethylpentatriacont-1-ene, R,R-35:1 showed the most activity. This is the first report of alkene-induced sexual activity in males of the genus Glossina.