Posted by Cathy Scott on September 12, 2016
Fruit flies love the smell of fruit, right? Maybe they love the fermentation products of the fruit [1,2,3]?
Possibly they really love to eat the yeast , and bacteria  that eat the fruit. Or are they attracted to the pheromones of the female fruit fly that is eating the fruit ?
As it turns out, they are attracted to all the above. The signature smells of alcohols and acids that Kombucha organisms give off while they are eating sugar is very similar to what happens to fruit as it sits out and eventually rots. Kombucha also contains the yeast and bacteria fruit flies crave as sources of protein. Thus doing a beautiful job of attracting Fruit Flies, all you need to kill them is a simple trap.
Traps can be made from straight active Kombucha or Kombucha with fruit, fruit juice or sugar. The benefit of adding sugar/fruit juice is that it really gets the yeast and bacteria growing and stirring up a bunch of yummy smells. The negative is that an active Kombucha will form a SCOBY (Symbiotic Colony Of Bacteria and Yeast) or Mother. Which will need to be removed occasionally.
All you need is:
Active Kombucha Culture (not pasteurized)
Fruit Juice, Fruit or Sugar (if desired)
Vessel (this can be anything from an old jar to a beautiful vase)
The best way to control fruit flies is to keep them in check. To do this make the trap or two at the first sign of fruit flies. When more fruit flies appear, check the trap remove the SCOBY and sometimes add a little more Kombucha, sugar or fruit juice.
The SCOBY can form a plug that can hinder the attractive compounds from actively disseminating into the air and luring the fruit flies. SCOBY will grow faster when you add fruit, fruit juice or sugar. Even without added sugar or fruit juice you still might need to remove the SCOBY occasionally.
Handling a SCOBY, especially a fruit fly encrusted SCOBY, can be a little too slimy for some people. Adding fruit is a little too much for me, it gets nasty, which can necessitate washing out the jar. You will have to assess your own level of fruit fly vs. gross tolerance.
It has been know for a while that vinegar (acetic acid) will lure fruit flies. In the quest for a better fruit fly trap scientists have found many chemical compounds associated with fermentation, nutrition and sex will entice fruit flies [1-6]. Kombucha fermentation produces an alluring mixture of the fermentation and nutrition compounds. All that is missing is the fruit fly sex pheromones. They show up when you start trapping flies.
1. Kleiber, J.R., et al., Attractiveness of Fermentation and Related Products to Spotted Wing Drosophila (Diptera: Drosophilidae). Environmental Entomology, 2014. 43(2): p. 439-447.
2. Dong, H.C., et al., A four-component synthetic attractant for Drosophila suzukii (Diptera: Drosophilidae) isolated from fermented bait headspace. Pest Management Science, 2014. 70(2): p. 324-331.
3. Becher, P.G., et al., Flying the Fly: Long-range Flight Behavior of Drosophila melanogaster to Attractive Odors. Journal of Chemical Ecology, 2010. 36(6): p. 599-607.
4. Christiaens, J.F., et al., The Fungal Aroma Gene ATF1 Promotes Dispersal of Yeast Cells through Insect Vectors. Cell Reports, 2014. 9(2): p. 425-432.
5. Robacker, D.C., Chemical ecology of bacterial relationships with fruit flies. Bulletin OILB/SROP, 2007. 30(9): p. 9-22.
6. Grosjean, Y., et al., An olfactory receptor for food-derived odours promotes male courtship in Drosophila. Nature, 2011. 478(7368): p. 236-U123.