While lethal, Erythritol was found in that study to take three days or so to kill adult flies. Results from the study showed that it could actually be an effective form of fly birth control. Egg-laying by adult flies was significantly reduced on the day they were fed erythritol. After that day, the adult flies were fed regular food. The day after being fed erythritol, flies egg-laying began to recover, and by the second day of normal food, they were laying eggs at the same rate as flies who’d never been fed erythritol.