Humans have spent a lot of time figuring out ways to get animals to ejaculate. They have fashioned artificial vaginas, inserted electric probes, and donned helmets that encourage birds to hump their heads. Now, Shir Zer-Krispil, from Bar-Ilan University in Israel, has developed perhaps the greatest technique of all: She genetically engineered flies to automatically ejaculate whenever they walk under red light.
The male insects have specific abdominal neurons that trigger the release of sperm by producing a chemical called corazonin (so named because it also makes insect hearts beat). Usually, corazonin-making neurons only fire after a complicated courtship ritual that involves chasing, stroking, singing, and eventually mating. But Zer-Krispil dispensed with all that lead-up by putting those neurons under the control of a red-sensitive protein.
Thirty seconds after the engineered males walk into a red-lit chamber, their abdomens curl up and they ejaculate. And then, they do it again. It happens seven times a minute, for up to three minutes. The flies had the option of walking into an unlit part of their chamber, but once they entered the red-light district, they tended to stay there.
Why red? First, it passes through living tissues easily, so even an overhead lamp can trigger neurons nestled deep within a fly’s body. Second, flies can’t see red, so it’s clear that their movements aren’t due to any visual attraction. Third ... it’s fitting? “We definitely thought about that,” says Galit Shohat-Ophir, who led the work.