Whether you headed to the beach, the mountains or the backyard chances are your summer included mosquitos! Mosquitos are a group of 3,600 fly species all belonging to the family Culicidae. While only a small subset (~6%) of this group bite, these bites can be incredibly serious.
In some areas of the world, mosquito bites simply leave the victim with a temporary itch. However, in other areas, mosquito bites are debilitating and even deadly. That’s because biting mosquitos carry dangerous diseases including Malaria, Filariasis, Yellow Fever, West Nile, Dengue Fever, Zika, and Chikungunya. It’s estimated that mosquitos are responsible for 1,000,000 deaths a year. This number makes them the most dangerous animal on earth!
Humans have been fighting mosquitos since antiquity. Archeologists found evidence that pharaohs slept under mosquito nets! Today, insecticide-treated bed nets are still an important first line of defense saving around 4.5 million lives. Window screens, the elimination of still water breeding places, and the application of repellents and insecticides are other popular control methods.
Biotechnology is also playing a huge role in combating mosquito-borne diseases. To ‘celebrate’ World Mosquito Day (August 20th) we’re highlighting five biotech strategies aimed at controlling these dangerous organisms.
Teaming Up with Predators: Mosquitos aren’t the only ones doing the biting. Fish, dragonflies, copepods, lizards, birds, and bats all count mosquitos as an important food source. Since the 1950s scientists have been working to identify native predators who specialize in mosquito consumption as a method of control. Check out this study investigating gecko as potential mosquito fighter.
Teaming Up with Parasites: Many mosquito predators are generalists that can only slightly reduce mosquito populations. Introducing or even increasing the number of these larger predators can also negatively effect an ecosystem. Consequently, scientists have turned to smaller and more specialized mosquito enemies. Two widely used biological controls are the nematode parasite Romanomermis culicivorax and the parasitic fungus Entomophthora culicis. Read more about the latter in this New York Times article.
Bacteria to the Rescue: This method adds one extra wrinkle to the “enemy of my enemy is my friend” approach. Wolbachia is an inter-cellular bacteria species found in over half of insect species. In mosquitos, it causes few if any symptoms. However, the do bacteria interfere with the transfer of diseases from mosquitos to humans. In a 2021 case study, introducing Wolbachia to local mosquito populations reduced dengue transmission in the region by 77%! Furthermore, because mothers pass the bacteria to their offspring, the infection stays in the population. This means a single treatment can last many years. However, the initial treatment is costly and time intensive as researchers must inject the bacteria into minuscule mosquito eggs.
Sterile Insect Technique: Several insect species including the screw-worm fly and Mexican fruit fly have been controlled by introducing a large number of sterile males into the wild. These males compete with native males to mate with females but produce no offspring. Over time this can cause large population declines or even complete eradication. However, accomplishing permanent population reduction requires many generations of mosquito rearing and introduction. Also, separating out female mosquitos (the ones who bite) continues to be a large hurdle. Read more about the successes and challenges of this approach on the WHO site.
Changing Mosquito Genes: This is the strategy that’s been making headlines this summer because of a large-scale study currently happening in Florida and California. The UK company Oxitec used CRISPR-based technology to create male mosquitos that have a ‘self-limiting’ gene as well as a gene that makes individuals more susceptible to certain insecticides. The self-limiting gene kills any female progeny in an early larval stage. If the offspring is male, it survives and becomes a carrier of the gene for the next generation. This summer the EPA approved a case study test of this approach. Learn more about the study and the technology with this Smithsonian Magazine article, this Mashable article, or this Vox video.