Any Stevia-Based Sweetener
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Stevia-based sweeteners like Truvia contain the ingredient erythritol. It has been proven to kill fruit flies. You can sprinkle some in your traps, or into fruit bowls. You can also sprinkle it around the house boundaries to act as an invisible shield against fruit flies, and possibly other insects as well. It is speculated it to become an eco-friendly insecticide. Truvia is one of the more popular sweeteners available in the US. It is not to be confused with the stevia plant, which has two sweet compounds, stevioside and rebaudioside A. Truvia only contains amounts of rebaudioside A, and is not linked to any health benefits. But it will kill and deter fruit flies.