No Sex for Males Without Taste

For the first time, researchers have linked a specific sex behavior to a female insect pheromone.

If you haven’t yet heard of pheromones, rest assured that the perfume industry has. Pheromones are chemical signals exuded by many animals — including humans — that evoke behavior. Sexual behavior.

The trouble is, nobody is quite sure which pheromones do what. That is fast changing, although not as fast as some Internet perfume ads would have you believe. Why? Human sexual behavior is so complex that it’s hard to tease out one sex signal from another.

Fruit flies are a lot easier to understand. So Hubert Amrein, PhD, and colleague Steven Bray started there. They took a close look at fruit-fly mating behavior. It’s got six steps — and they have to be danced in exact order, although repetitions are allowed:

1. The male finds a female and gets into the right position to begin the mating ritual.
2. Using his front two legs, the male taps the female on the abdomen.
3. The male sings a courting song to the female by buzzing his wings.
4. The male licks the female.
5. The male curls his abdomen in a mounting attempt.
6. The male succeeds in mounting and copulation occurs.

Then, Amrein and Bray took a closer look. Fruit flies, they knew, have taste buds on their legs. When they analyzed those taste buds, they found that the flies’ front legs had special taste buds. They acted as receptors for female insect pheromones. This means that when they taste the female insect pheromone, they send a chemical signal to the brain.

The researchers found the gene responsible for the special front-leg pheromone taste buds. Then they raised male fruit flies that lacked the gene. This meant they had no pheromone tasters on their legs.

The tasteless males tried to have sex. But when they got to step 2 — tapping the female’s abdomen — they stalled out. Unable to taste the female insect pheromone, they didn’t know to when to sing their mating song. They kept trying, but kept failing. Eventually, the females got bored and flew away.

What does this mean? It’s a sign that researchers are a step closer to decoding the chemical signals that make us want to act in certain ways. Perfume makers, stay tuned.

The findings appear in the Sept. 11 issue of Neuron.