Good Fruit Grower

May 15

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28 MAY 15, 2014 GOOD FRUIT GROWER Cherries A better FLY TRAP U .S. Department of Agriculture scientists have developed a chemical lure for the spotted wing drosophila that is more effective, consistent, and longer lasting than standard food baits and makes traps easier to service. Growers have been using wine and/or vinegar in traps to monitor the insect. The flies are attracted by the odor, drown in the liquid, and can then be identified and counted. A drawback of this approach is that the volatiles in wine and vinegar quickly dissi- pate, so that the trap soon loses its attractiveness and is not consistently attractive over time. Another problem is that the wine and vinegar attracts many other insects, so that identifying spotted wing drosophila (Drosophila suzukii) in the liquid can be tedious and messy. The fly is only 2.0 to 3.5 millimeters long—the same size as its close relative, the common vinegar fly (Drosophila melanogaster). Merlot In an effort to design a better fly trap, Dr. Peter Landolt and Dr. Dong Cha at the U.S. Department of Agriculture's laboratory in Yakima, Wash- ington, set out to identify the specific components of wine and vinegar that the spotted wing drosophila found most attractive. Landolt, research leader at the lab and an expert on insect attractants, had already done research showing that spotted wing drosophila flies preferred Merlot to other wine varieties, that they preferred rice vinegar over other types of vinegar, and strongly preferred a mixture of the two materials. It is thought that the insect is actually looking for a source of sugar, but since sugar is not volatile (has no smell), it orients to the strong smell of fermented fruit products that are rich in sugars. It may be attracted to the yeast that ferments the fruit, which is also a part of its diet. Insects detect odors with receptors on their antennae. For the experiments, Landolt and Cha mounted a tiny elec- trode either against the neural lobes on the back of the severed head of a spotted wing drosophila or on a freshly plucked antenna so that electrical signals from the receptors could be recorded and magni- fied as they detected volatile chemicals in wine and vinegar. At the same time, they used gas chromatography and mass spectroscopy to identify the chemical components in the wine and vinegar that elicited responses from the antenna. After being detached from the body of the insect, an antenna remains responsive for about a day, Cha told Good Fruit Grower. During a series of such experiments, fly antennae detected 13 chemical components of the very complex bouquet of wine and vinegar. The next step was to expose live flies to those chemicals in lab assays to find out which chemicals attracted the flies and which repelled them. Combinations of the attractive chemicals were then tested in traps in the field and compared with a wine-and-vinegar bait. The scientists found that the most attractive chemicals were acetoin and methionol, combined with pure ethanol and acetic acid. The next step was to develop a dispenser that would release the four chemicals consistently in a trap over a long period of time. If a grower wants to interpret trap catches, the attractiveness of the trap must be stable, Landolt said. USDA researchers identified specific volatiles that attract spotted wing drosophila. by Geraldine Warner "Now, we're quite a bit better than wine and vinegar consistently." —Dr. Peter Landolt

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