Sexually frustrated male flies turn to drink, scientists find

In a new study, scientists have found that male flies that are deprived of sex, and more specifically of ejaculation, consume more alcohol, while repeated, ‘successful encounters’ can actually reduce their thirst for booze.

The study, entitled ‘Ejaculation Induced by the Activation of Crz Neurons Is Rewarding to Drosophila Males’ and published in the journal Current Biology on 19 April, found that sexually deprived male flies of the genus Drosophila consumed more alcohol, while those on the opposite end of the scale consumed less alcohol.

The scientists induced ejaculation by activating Crz neurons which is said to “mimic mating reward in Drosophila”. This was achieved through the use of optogenetic tools, which stimulates neurons that have been genetically modified to respond to light.

In this case, the team used a red light which they shone into one side of the enclosure housing the flies. They noted that the flies spent a lot of time in the ‘red light section’ indicating that they liked the sensation of ejaculation.

Repeated activation of the Crz neurons also reduces ethanol consumption, according to the study’s authors.

Galit Shohat-Ophir, co-author of the paper and a researcher at Bar-Ilan University in Israel, explained: “Successful mating is naturally rewarding to male flies and increases the levels of a small peptide in the brain called Neuropeptide F. Male flies that are sexually deprived have increased motivation to consume alcohol as an alternative reward”.

The scientists then trained the flies to associate the red light and ejaculation with a particular odor. Once again, the flies preferred to loiter in the area where the scent was strongest.

The flies were then given a choice of liquid food with one sample containing no alcohol and another with a proportion of ethanol. Those flies that had not been exposed to the red light opted for the alcohol-laden food, while those that were ‘sexually satisfied’ went for the normal, non-alcohol food.

The paper also stated: “Sexual interactions with female flies that do not reach copulation are not sufficient to reduce ethanol consumption, suggesting that only successful mating encounters are rewarding”.

Drosophila, often referred to as ‘small fruit flies’, are noted for the way they linger around overripe, fermenting or rotting fruit.