Mutant Mosquitoes Lose Lust for Human Scent

SCIENCE

Mutant Mosquitoes Lose Lust for Human Scent
Biologists have engineered a mutant strain of mosquitoes that lack the ability to sniff out human beings. Or insect repellent.

Discussion Ideas:

• There are more than 3,000 species of mosquitoes in the world. Why do students think the scientists featured in the Nature article chose to study the species Aedes aegypti?
  • They’re not hard to find. Aedes aegypti are very common mosquitoes that inhabit tropical and subtropical regions around the world. 
  • They’re dangerous. A. aegypti themselves do not pose a threat to human beings—other than irritating itches. However, these mosquitoes are vectors for several deadly diseases. A vector is an organism that carries and transmits a germ or disease to another organism. A. aegypti are vectors for viruses causing dengue fever (millions of infections, 25,000 deaths every year), chikungunya (millions of infections every year), and yellow fever (200,000 infections, 30,000 deaths every year). In fact, A. aegypti is commonly called the “yellow fever mosquito.” Genetically modifying A. aegypti mosquitoes could reduce the serious health risk they pose to people (especially children) in tropical and subtropical regions of the world.
• Read our media spotlight on “Insecticide-Treated Nets,” which outlines the most effective way to combat malaria, a disease carried by mosquitoes that claims the lives of about 665,000 people every year. What impact do students think the experiment featured in the Nature article will have on populations threatened by malaria?
  • Not much, at least right now. 
    • The experiment didn’t prevent mosquitoes from feeding on human beings. The mosquitoes’ sense of smell is “important for picking between hosts, but not for finding and feeding on them,” the Nature article says. (The hosts in the Nature experiment were people and “our beloved guinea pigs.” In Africa, hosts include people, pets, and livestock.) Human communities would be less at-risk among a genetically altered mosquito population, but still at risk. ITNs (insecticide-treated nets) would still be the most effective barrier to malaria and other mosquito-borne diseases.
    • The experiment targeted a different species of mosquito (A. aegypti) than the one that carries malaria (Anopheles gambiae), although the gene targeted by biologists (orco) exists in both species and can be targeted in the same way.
    • The biology and logistics for widespread genetic engineering of these mosquitoes is still a long way away. Even if biologists were able to prevent mosquitoes from biting human beings, can students think of some logistical obstacles to introducing that genetically engineered population into the wild?
      • Scientists would need to work with local, regional, and national governments to introduce a genetically modified organism (GMO) into the wild. Many communities reject GMOs in foods, and may be suspicious of other GMOs. 
      • What would be the ecological impact? What food webs are mosquitoes a part of, and how would organisms that prey on mosquitoes (such as fish or birds) be affected? (Don’t leap to conclusions, conservationists . . .)
      • The plan to safely introduce the genetically altered species may be expensive. Who would bear the cost?
• “We’re not looking to kill these insects, per se, we just want them to feed on something else,” says one researcher in the Nature article. Why don’t we want to kill these insects? Can students think of why we would not want to eradicate disease-carrying mosquitoes?
  • Surprisingly, scientists really can’t! This fascinating 2010 Nature article outlines the ecological consequences of mosquito eradication—including a human population that is healthier and economically stronger. “Ultimately,” the article concludes, “there seem to be few things that mosquitoes do that other organisms can’t do just as well—except perhaps for one. They are lethally efficient at sucking blood from one individual and mainlining it into another, providing an ideal route for the spread of pathogenic microbes.”