- Author: Mark Bolda
It is becoming increasingly evident that monitoring for spotted wing drosophila (SWD) is an integral part of a program to manage this fly to non-damaging levels. Growers who are aware early on that SWD has entered their field maintain a wider range of options than those who suddenly find themselves confronting a very heavy infestation with a lot of infested fruit.
Recall from the previous post that an interest in alternatives to GF120 Fruit Fly bait being used as a trap, either because of a lack of efficacy, cost or just plain curiosity in what will work sparked an effort to test other materials.
A further screen of materials has recently been pursued also by my private industry colleague. He made purees of peach, nectarine, orange, pineapple, beer + banana and added an amount of yeast to each one. One further treatment was a mixture of yeast, sugar and water (one packet baker’s yeast 0.25 oz, 4 teaspoons sugar and 12 fl oz water distributed among 5 or 6 Mason jars). Each of these was placed in a field having significant SWD activity.
While the fruit and yeast mixtures did catch flies to a certain extent, the mixture of yeast, sugar and water was by far the most successful. The yeast, sugar and water mixture is also very attractive to people because it is very clear and allows for easy viewing of trapped flies. Indeed in a further test comparing yeast, sugar and water mixture to GF120 traps (1 part GF120 to 4 parts water), found that it was far more attractive to SWD and vinegar flies. This success has been replicated by several area growers as well.
Some conjecture and comment about the yeast, sugar and water mixture.
While the GF120 trap mixture worked in the winter and to a certain extent in the spring, it may be that during the fruiting season the smell of this material is being masked by the abundance of other food scents coming from fruit and flowers. As anglers well know, fish change their preferences over the course of the season, and it the possibility that SWD is doing the same is difficult to deny.
Why the strong attraction to a yeast and sugar bait? There has been some amount of thinking determining that the yeast consuming the aqueous sugar is releasing plumes of carbon dioxide which is attracting SWD. While this may be true for the first 24 hours, it appears that the trap is most effective AFTER most of the sugar has been consumed, so it is apparent that the smell of fermentation is what is pulling the flies.
One positive addition to the yeast, sugar and water bait trap would be a material to keep the flies there once they have flown within the confines of the jar or bottle. There have been some comments from users noting the high level of attractiveness of this material is partly undone by the ability of flies to escape. Unlike GF120, there is no poison or surfactant which breaks the surface tension of the water to the point where flies alighting upon it fall on down into the liquid rather than still be able to walk on the surface. This is something worth looking into at a later date.