The reasons why mosquitoes are so attracted to human blood have been a mystery until now. However, a new study may provide answers to this question. Published in the journal Proceedings of the National Academy of Sciences (PNAS) on Monday (1st), the work suggests that a pair of hormones may work together to activate or suppress mosquitoes’ desire for blood.
The females of most insects, including Aedes aegypti — which carries the dengue, chikungunya and Zika viruses — feed on animal blood (including humans) to develop their eggs. However, after this consumption, their appetite for blood reduces until after the females lay their eggs.
The researchers wanted to understand the mechanism behind this cycle. They noticed that levels of a hormone produced in the insect’s gut (called neuropeptide F, or NPF) increased when the mosquitoes were searching for a host and disappeared after they had fed on blood.
“This motivated us to look at whether the presence of this hormone was a determining factor in seeking a blood meal,” Michael Strand, an entomologist at the University of Georgia in Athens and study leader, told Nature.
The team then analyzed mosquito enteroendocrine cells, which produce hormones in the gastrointestinal tract. As expected, NPF levels spiked before the mosquitoes had a blood meal and dropped six hours after feeding.
According to the researchers, the mosquitoes’ attraction to human blood corresponded to this hormonal fluctuation: they showed no interest in a human hand on the day they had eaten; however, after laying their eggs, they felt attracted to it again.
Scientists later knocked out the gene that produces NPF in female mosquitoes and found that this reduced their attraction to human blood. When they injected the hormone back into these mosquitoes, their interest was restored, but it had little effect on mosquitoes that were carrying eggs.
In parallel with these findings, the researchers identified another hormone, called RYamide, which is also produced in the intestine and is responsible for regulating feeding behavior in insects. After a meal, levels of this hormone increased.
In eggless mosquitoes, an injection of RYamide reduced NPF levels and suppressed their attraction to human hosts. Mosquitoes with natural levels of the hormone, on the other hand, darted toward a human hand. According to the researchers, this behavior suggests that the two hormones work together to stimulate and suppress the mosquitoes’ attraction to human blood.
“The discovery may provide new pesticide targets to prevent mosquito breeding and disease transmission,” Zhen Zou, an entomologist at the Institute of Zoology of the Chinese Academy of Sciences in Beijing, tells Nature.
Source: CNN Brasil
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