Why do flies congregate at rotten fruit?
Partly because when male fruit flies detect food odors, they release a pheromone that encourages female flies to come and mate.
Animals rely on their sense of smell to navigate their environments; for example, the smell of food attracts animals to particular locations. These food-rich sites are also popular places for meeting, mating, and rearing offspring. Scent molecules emitted by animals can also attract others to a particular location or affect their behaviour. These molecules are known as pheromones.
Little is understood about how cues from food and pheromones interact to influence animal behavior. Studies of the Drosophila species of fruit fly have been conducted to tease out these interactions. Fruit flies are attracted to the smell of food — particularly overripe or rotting fruit — and often congregate at a food source to mate and lay their eggs. But whether it is the food itself or other cues that trigger these behaviors is not clear.
Now, Chun-Chieh Lin and colleagues reveal that male fruit flies emit a pheromone in response to the smell of food. This pheromone attracts females to the food to mate and encourages the females to lay their eggs at the food-rich site. This allows the male fly to have some say as to where his offspring will be laid and also increases the chances that his offspring will survive.
Using genetic and other experiments, Lin and colleagues found that the pheromone is detected by a receptor on the antennae of the female flies. This stimulates a specific type of brain cell that causes the female to lay her eggs at the site where the pheromone has been deposited. A chemical released by rotting fruit also stimulates these receptors and encourages the females to congregate and lay eggs.
The body of a male fly is coated by many different pheromones, yet he deposits only a select few upon smelling a food odor. How this occurs remains to be determined, but suggests that different pheromones might be localized to different body parts. By rubbing just those parts onto their surroundings, the male might be able to deposit a specific pheromone. How food odors specifically trigger this response, or if other flying insects also deposit pheromones in response to food odors, remains to be determined.
To find out more
Read the eLife research paper on which this eLife digest is based: “Food odors trigger Drosophila males to deposit a pheromone that guides aggregation and female oviposition decisions” (September 30, 2015)
