We've been breeding the fly Drosophila melanogaster in the lab for decades. We've tinkered with their genes — giving them extra legs, curly wings, or odd coloured eyes — in pursuit of understanding genetic inheritance and how tissues develop. But until now we didn't know which chemical made them start to mate.
Image: Anna Schroll | Max Planck Institute for Chemical Ecology
However, we did know which neurons in a fly's brain responded to this unknown sex pheromone. Scientists at the Max Planck Institute for Chemical Ecology in Jena, Germany used this circuit as a litmus test for fly odours: first isolating and separating chemicals from the surface of the fly exoskeleton, then testing each one to see whether it made the pheromone-sensitive neuron active. They found only one chemical got a strong response: a fatty acid called methyl laurate.
Methyl laurate is a very common chemical: people use it as a lubricant, as a surfactant in detergents, or as an inert base for perfumes. In Drosophila melanogaster, the chemical triggers male courtship behaviour, and also sets off another set of neurons that make the flies move toward the odours of other flies. Markus Knaden, who led the studies, explains, "The novel pheromone activates two different circuits: One is involved in courtship and mating of males and females, the other one in aggregation."
Every species of Drosophila that the team tested secreted methyl laurate, suggesting that the pheromone has been an important part of the flies' mating system for a very long time. That may eventually lead to some practical applications: if the Drosophila species that are agricultural pests are as sensitive to methyl laurate as the species we use in the lab, the chemical's winey scent could eventually turn up as bait for fly-specific pheromone traps.
Read the study here: Dweck et al. 2015