Mosquitoes and the burden of disease they cause continue to weigh down many communities around the world. Despite their fragile appearance, mosquitoes continue to resist our best efforts to eliminate them. We’ve drained and polluted their wetland homes, and we’ve filled the skies with clouds of insecticides, but still they persist.
There is no reason why mosquito-borne disease won’t continue to spread in the decades ahead. While climate change, urbanisation and globalisation will all influence future mosquito-borne disease risks, some of our current control products are also losing their potency.
In many ways, our efforts to control mosquitoes have also been our undoing. We constantly underestimate the resilience of mosquitoes. The more insecticides we use to try and kill mosquitoes, the greater the likelihood they will develop resistance to these chemicals. We need to look at alternative ways to control mosquitoes, and a new project pitting mosquitoes against mosquitoes is being trialled in Australia.
Bugging the mosquito
While there are thousands of mosquito species worldwide (over 300 in Australia alone), the yellow fever mosquito (Aedes aegypti) is of greatest concern when it comes to outbreaks of dengue, chikungunya and Zika viruses. Second on the list is the Asian tiger mosquito (Aedes albopictus), a severe pest that also transmits these viruses. These two exotic mosquitoes have proven great at invading the world, spreading outwards to live with us in our cities. And they do love biting people.
It is important to remember that only female mosquitoes bite in pursuit of blood. Male mosquitoes do not, feeding only on nectar.
New approaches using an insect-specific bacteria have been developed that can sabotage mosquito populations. This works by either disrupting their reproduction or blocking their ability to transmit pathogens.
Scientists have concentrated their research on a naturally occurring insect bacteria, Wolbachia.
Wolbachia doesn’t naturally infect all mosquitoes. However, studies have shown female mosquitoes infected in a laboratory with Wolbachia pass the infection through to their eggs. Then when males infected with the bacteria mate with uninfected females, the female’s eggs do not hatch. The reasons for this are not yet fully understood but is known as “cytoplasmic incompatibility”.
Male Wolbachia-infected mosquitoes reared in the laboratory can be released into the field. As females only mate once, each successful mating results in no eggs hatching in the next generation. Therefore, the mosquito population shrinks over time.
Given these frisky male mosquitoes are better at finding female mosquitoes than we are with our insecticides, this approach could be a winner. It avoids increasing the risks of insecticide resistance and reduces the risks of other species in the area being impacted by insecticides.