Humans are constantly engaged in an evolutionary arms race with pathogens. We spend years developing drugs, such as antibiotics or antivirals, only for resistance to rapidly appear. The same thing happens when we confront troublesome weeds with herbicides, or crop-ravaging insects with pesticides. Now, humans have been dealt another devastating blow with the emergence of a hybrid malaria mosquito that is resistant to the insecticides on treated bed nets. What’s more, scientists believe that the introduction of these nets could have promoted the emergence of these hybrid “super mosquitoes.”
This worrying situation is occurring in Mali, West Africa, which has been struggling with malaria for many years. Because malaria is transmitted by mosquitoes, it is a preventable disease which also has the potential to be eradicated. Since 2000, malaria mortality rates have fallen by 47% globally, and by 54% in Africa. This is partly due to the use of insecticide-treated mosquito nets which prevent people from being bitten.
Millions of these mosquito nets are delivered yearly, including to Mali, and they have been a huge success. But unfortunately, in 2006, Mali’s malaria situation began to worsen. Scientists noticed that a malaria-carrying mosquito species, Anopheles coluzzi, was becoming increasingly resistant to insecticides. In order to find out how these resistance genes could have arisen, scientists examined the DNA of both this species and another malaria vector, Anopheles gambiae.
As described in Proceedings of the National Academy of Sciences, they found that the mutations conferring resistance in A. coluzzi were the same gene variations previously only found in A. gambiae. This was a strange observation due to the fact that these species do not usually interbreed, and the resulting hybrids usually die without reproducing, The Verge reports. However, it was evident that the mutations in A. coluzzi started to appear when the two species began interbreeding. What’s more, the emergence of these hybrids seemed to coincide with the introduction of the insecticide-drenched nets.
Although a correlation cannot prove anything, the evidence presented could suggest that the mosquito nets played a major role in driving hybridization between two different species, which ultimately led to the emergence of “super” resistant hybrid mosquitoes.
“A man-made change in the environment—the introduction of insecticides—has altered the evolutionary relationship between two species, in this case a breakdown in the reproductive isolation that separates them,” said lead researcher Gregory Lanzaro. “What we provide in this new paper is an example of one unusual mechanism that has promoted the rapid evolution of insecticide resistance in one of the major malaria mosquito species.”
But this shouldn’t deter people from using insecticide-soaked nets, because they have saved thousands, possibly even tens of thousands of lives in Mali alone. What the study does highlight, however, is the urgent need for new effective control strategies, a number of which are already in development. Some companies, for example, are genetically modifying mosquitoes so that they are no longer able to transmit disease.