Medical News
Asian tiger mosquitoes can spread dengue and chikungunyaKevin Frayer/Getty
By Michael Le PageThe number of biting female Asian tiger mosquitoes, which spread diseases such as dengue and chikungunya, has been reduced by more than 80 per cent at two small sites in Guangzhou, China, by a new “sterile male” method developed by Zhiyong Xi of Michigan State University.
Sterile male methods involve releasing large numbers of infertile male insects to cause a population crash. The Guangzhou trial is the latest of many to show that several variants of such methods can be highly effective for controlling insects.
Using parasites
One variant uses a common parasitic bacterium called Wolbachia. When males infected with Wolbachia mate with females that aren’t infected with the same strain, the parasite somehow prevents them from producing offspring.
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This means releasing male mosquitoes infected with a Wolbachia strain not found in local mosquitoes has the same effect as releasing sterile males. This approach has proven successful in several trials around the world, most recently in Miami.
The China trial involved mosquitoes infected with three strains of Wolbachia, because the Asian tiger mosquito, Aedes albopictus, is already infected with two strains.
Removing females
The problem with using Wolbachia is that, if any female mosquitoes infected with the added Wolbachia strain are accidentally released, these can breed with the released males and the method will stop working.
It is possible to remove around 99 per cent of females mechanically, because they are larger at the pupal stage. But all the remaining pupae usually have to be screened by eye to remove the final few females, which is expensive.
However, Xi’s team have now shown that a low dose of radiation can sterilise any remaining females without weakening the males. This can replace manual screening, making it easier and cheaper to scale up production. “Our approach is much more cost-effective,” Xi says.
Small trials
Sterile male approaches should be more environmentally friendly than keeping mosquito numbers down using pesticides, as only the target species is affected. However, such techniques have yet to be used on a large scale for tackling mosquitoes.
“These methods have not had anywhere near the uptake that their success in field trials would warrant,” says Luke Alphey of the Pirbright Institute in the UK.
Xi says there are plans to use the Wolbachia and radiation combination method to tackle Aedes mosquitoes in Mexico, Singapore, Taiwan and Australia, and to eradicate the Culex mosquitoes devastating bird populations in Hawaii. The team has also begun to develop the method for the Anopheles mosquitoes that transmit malaria.
Many disease-spreading mosquitoes are invasive species in most countries, so eradicating them shouldn’t disrupt ecosystems.
Journal reference: Nature, DOI: 10.1038/s41586-019-1407-9
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