What drives mosquitoes’ bloodlust?
Their hormones
蚊子为什么嗜血？
根源在激素
One hormone seems to boosts the insects’ thirst for a blood meal, while another shuts it off.
一种激素似乎增强了蚊子对血的欲望，而另一种激素则能抑制这种欲望。
A pair of hormones work in tandem to activate or suppress mosquitoes’ cravings for blood, according to a study published today.
今天发表的一项研究显示，一对激素协同作用能激发或抑制蚊子对血液的渴望。
The findings reveal a possible mechanism for what drives mosquitoes’ attraction to people and other animals, which has remained a mystery until now. “The discovery could provide new pesticide targets for preventing mosquito reproduction and disease transmission,” says Zhen Zou, an entomologist at the Chinese Academy of Science’s Institute of Zoology in Beijing.
这些发现可能揭示了蚊子吸引人类和其他动物的机制，但这一点至今仍是个谜。中国北京科学院动物研究所昆虫学家邹震（音译）说：“这一发现可以为防止蚊子繁殖和疾病传播提供新的杀虫剂靶标。”
The females of most mosquito species-including Aedes aegypti, the carrier of the viruses that cause dengue fever, yellow fever and zika-feed on animal blood for the development of their eggs. But once they’ve eaten a blood meal, their appetite for blood shuts down until after they lay their eggs.
大多数雌蚊——包括导致登革热、黄热病和寨卡病毒的携带者埃及伊蚊——都以动物血液为食，以促进卵的发育。但一旦吸过血，直到产卵之后它们才会对血有食欲。
Michael Strand, an entomologist at the University of Georgia in Athens, wanted to better understand the mechanism that controls this cycle of attraction. He noticed that the levels of a hormone produced in the insect gut called neuropeptide F (NPF) spiked when mosquitoes were seeking a host and disappeared after they feasted on blood. “That motivated us to look at whether this hormone’s presence was a driving factor in seeking a blood meal,” says Strand.
雅典佐治亚大学的昆虫学家迈克尔·斯特兰德想更好地了解控制吸引循环机制。他注意到，当蚊子寻找宿主时，肠道中产生的神经肽F（NPF）激素飙升，而当蚊子吸满血液后，这种激素就会消失。斯特兰德说：“这促使我们研究这种激素是否是蚊子寻找血液的驱动因素。”
With his colleagues, Strand analysed mosquito enteroendocrine cells, which produce hormones in the gastrointestinal tract. As expected, NPF levels skyrocketed before mosquitoes had a blood meal and fell six hours after they fed. The mosquitoes’ attraction to humans matched this hormonal swing: they showed no interest in a human hand on the day of their meal, but made a beeline for it after they had laid their eggs. “There was this almost perfect mirror image,” says Strand.
斯特兰德和他的同事分析了蚊子的肠内分泌细胞，这种细胞在胃肠道中产生激素。不出所料，NPF在蚊子吸血前飙升，而在吸血6小时后下降。蚊子对人类的吸引力与这种激素波动相吻合：蚊子在进食当天对人手不感兴趣，但在产卵后会径直走向它。斯特兰德说：“这几乎是完美的镜像。”
Next, the researchers knocked down the gene that produces NPF in female mosquitoes and found that it reduced their attraction to humans. When they injected the hormone into these mutant mosquitoes, it restored their interest in humans but had little effect on mosquitoes that were carrying eggs.
接下来，研究人员去除了雌蚊体内产生NPF的基因，发现它减少了蚊子对人类的吸引力。当他们将激素注射到基因突变蚊子体内，它又对人类感兴趣，但对携带卵子的蚊子几乎没有影响。
The team also found that certain neurons that reach into the gut produced another hormone called RYamide, which regulates feeding behaviour in insects. Just as NPF levels dropped after a blood meal, RYamide levels increased. In mosquitoes without eggs, an injection of RYamide reduced their NPF levels and suppressed their attraction to human hosts, whereas the control mosquitoes-with natural hormone levels-zipped towards a human hand. This suggests that NPF and RYamide work together to stimulate and suppress host attraction in mosquitoes.
研究小组还发现，某些进入肠道的神经元产生RYamide激素，它调节蚊子的进食行为。吸血后，NPF下降，RYamide增加。在无卵蚊子中，注射RYamide降低了它们的NPF，抑制它们对人类宿主的吸引力，而对照组蚊子——具有天然激素——则会飞向人手。这表明，NPF和RYamide能共同刺激和抑制蚊子对宿主的吸引。
Strand and his colleagues plan to investigate other molecular factors that are involved in host attraction to build a more complete picture. “Life is never simple,” he says.
斯特兰德和他的同事计划对参与宿主吸引的其他分子因素进行研究，以建立一个更完整的图景。他说：“生命从来都不简单。”
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