The use of natural (non-synthetic) chemicals to influence insect behaviour is likely to be well known, in one way or another. Those troubled by mosquitoes are likely to have tested the hypothesis that citronella oil-based candles are repellent to mosquitoes, with varying degrees of success. Those who have tried to control fruit-flies may well have tried protein bait traps whose "scent" lures flies to a pesticide-containing solution, and so to their deaths; the attractant, to which both males and females respond, is a complex mixture of chemicals derived from the breakdown of the protein - commonly brewers yeast. Another "natural" fruit fly attractant is a single chemical, methyl eugenol, a component of many flower fragrances. Only the males of many fruit fly species find it attractive, and it is used in monitoring and control programs