Male mosquitoes can also feed on our blood

The mosquito scourge could be even worse than we thought. Fascinating research published this month reveals that it’s not just women who can suck our blood: men can apparently do it too.

Scientists from Pennsylvania State University and other institutions made their case in a preprint. released last week on the bioRxiv website. Through various experiments and situations, they found evidence that some male mosquitoes reliably feed on blood, at least under the right circumstances. The findings could overturn a long-held belief about the threat these insects pose to humans, the researchers say, although additional research will be needed to better understand the phenomenon.

“We really need to look rigorously at what’s happening on the ground,” the study’s lead author, Jason Rasgon, an entomologist specializing in vector-borne diseases at Penn State, told Gizmodo.

A chance discovery

Adult male mosquitoes have long been thought to feed on nectar and other sugary sources for sustenance, while most female mosquitoes regularly feed on the blood of other animals for survival. And Rasgon and his colleagues weren’t initially looking to challenge these widely held assumptions.

A few years ago, however, one of Rasgon’s graduate students was conducting blood-feeding experiments with mosquitoes in the lab when she noticed that some of the insects being fed were males. Rasgon stopped the student from throwing away those mosquitoes. He remembered a article 2016 where researchers have attracted A five-faced mosquito males feed on blood; the blood proved toxic, killing males within days. Given the chance, he wanted to see if the same thing would happen with a different species, so the team simply kept an eye on them. To everyone’s surprise, their blood-drinking males lived as long as males on a typical sugar diet.

“A lot of science is like that. I always say that most of the great advances we’ve made in my 20 years as a scientist have been accidents. And usually scientific things start with, ‘Oh, that’s weird. What’s going on there?” Rasgon said. “And most people don’t follow up, but you have to follow up on them.”

At first, Rasgon thought their discovery was nothing more than a cool science note. But he and his team continued their research with their available resources. In one experiment, for example, they found that they could get males of certain species to regularly suck blood from an artificial feeder if the insects were first dehydrated – something they already showed would happen with females. They then created CRISPR-edited mosquitoes that lacked the ability to sense humidity. These males did not feed on blood, suggesting that dehydration is the key to causing blood feeding in males.

Rasgon also began discussing his work with other scientists in the field, who made their own contributions to the growing project. For example, some of the co-authors had collected blood-fed male mosquitoes in the wild (from Texas in the United States and Majorca in Spain). These wild mosquitoes tested positive for vertebrate (dog and human) DNA, indicating that they had successfully fed on animal hosts.

Additionally, the team’s experiments demonstrated that some male mosquitoes can be infected with the blood-borne West Nile virus. Worse yet, the virus can replicate sufficiently inside these males to potentially cause a new infection if transmitted to another host via blood feeding, they found.

In the trippiest part of this whole story, Rasgon used himself as bait. Luckily, he had been scratched by his cat a day earlier, leaving behind a wound that was beginning to crust over. He removed the scab and exposed his hand to a cage of 20 dehydrated male mosquitoes. Five of the males probed around the wound and one managed to feed on its blood. In another experiment, a male mosquito even managed to pierce Rasgon’s skin and provoke a typical immune response to the bite, but only for ten minutes (this mosquito, however, failed to find a blood-carrying capillary).

In total, the team found that at least five species of male mosquitoes (100 tarsals, 100 five-sided, Ae. Egypt, Ae. notoscriptus and An. of Stéphane) can feed on blood. And what started as a small original study written by three authors has now expanded to 17 authors from Germany, Spain, Australia and the United States (unfortunately, Rasgon’s cat does not appear to have been rewarded for their contribution).

What happens next?

As interesting as this may sound, researchers caution that there’s still a lot we don’t know about what’s going on here.

The team’s research suggests that the blood supply of male mosquitoes requires specific criteria, namely dehydration. This could mean that this behavior only rarely occurs in nature. At the same time, Rasgon notes that the real world is often harsh. So maybe many men are thirsty enough to try feeding blood through their trunks.

Another crucial unanswered question is whether male mosquitoes regularly transmit diseases to their hosts. Several of the species studied are common carriers of germs that make people sick. And even if men play only a small role in the transmission cycle, this role could be important enough to merit attention. The researchers note that sterile male mosquitoes are now used to combat mosquito-borne diseases like malaria – a strategy that may be riskier than currently thought.

“I went into this thinking it was a little bit stupid. And now I’m not so sure. I actually think it might be bigger than we gave it credit for before,” Rasgon said.

Rasgon and his team submitted their study to peer review, an essential part of reviewing any research. And they’re optimistic that their findings can spark more interest in solving the mysteries surrounding the vampiric habits of male mosquitoes.

“We need to do this in a rigorous way. We need real funding. Some pretty difficult ground work needs to be done,” Rasgon said. “Hopefully next year we can do it.”