Scientists have come out with an explanation to why male mosquitoes do not bite humans.

In a new study from Rockefeller University’s Leslie Vosshall lab, some researchers have found that although both sexes of mosquito share the same neurons and brain structures needed to find humans, the males cannot bite because they lack the specialized stylet to pierce the skin of humans.

In their findings published on Monday by phys.org, the researchers discovered that the biting hardware is hidden in the male mosquito brain, locked behind a simple genetic switch. They however noted that with mutation to the right gene, the male mosquitoes would begin buzzing toward human scents in search of a prize that they do not even want.

This new findings might also contribute to current understanding of how female mosquitoes spread malaria, a diseases that kills millions yearly.

Lead author of the study Nipun Basrur, a Ph.D. student in Vosshall’s lab while giving further perspective on this said, “This opens up a path into the mosquito brain. We really had no idea what circuits in the brain might dictate how female mosquitoes sense humans and make decisions to bite them. Now that we know which gene is controlling them, we can look inside the brain and investigate further.”

“For a long time, the assumption was that sex-specific behaviors came from sets of neurons entirely specific to that sex. But recent work, including our study, has shown that both sexes often have the same neurons and that genetics controls how they are used,” Basrur noted.

Basrur and colleagues began their work by examining a gene called fruitless, which is known to control courtship behavior in fruit flies. When they knocked out the analogous gene in male mosquitoes, these insects, like fruit flies, failed to mate effectively with females. But the scientists chose to investigate further, suspecting that the mutation might also impact male mosquitoes’ desire for blood.

When offered warm blood through a net, however, mutant males abstained just like non-mutant males, even as female mosquitoes partook. The new study found that, when exposed to body heat, females liked what they felt. Mutant males, true to their sex, remained unimpressed by the promise of a blood meal, suggesting the corrupted gene does not necessarily play a role in feeding behavior.

But when the scientists offered these mutant males a human arm, they suddenly swarmed. “This was a truly unexpected and spectacular finding. We had never seen males interested in the scent of a human before,” Vosshall, who is the Robin Chemers Neustein Professor as well as an HHMI investigator said.

Later tests confirmed that, while mutant male mosquitoes still lacked the desire to drink blood and the ability to sense body heat, turning off the fruitless gene had allowed their brains to process the unique smell of a live human—activating a repressed urge to seek out humans just like a female.

“This suggests that male mosquitoes actually possess the neural circuits required to hunt humans. Removing fruitless appears to reveal this latent behavior in males,” Basrur said.

This study may have provided a leeway on how to use this information to masculinize female mosquitoes, blocking their ability to spread disease, phys.org wrote.

Future studies from the Vosshall lab will investigate these latent neurons, continuing to explore how sex differences are encoded in the brain and determined by genes.

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