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Why is CSIRO releasing mosquitoes?

By , 19 July 2018

Image of two mosquitoes.

The male on the left won’t bite, but the female on the right certainly will! Image: CSIRO

There are plenty of reasons to hate mosquitoes. They are annoying, hard to catch, and their bites can itch for days. But they’re not just irritating – in many places they spread diseases such as malaria, Zika and dengue.

Mosquitoes infect around 700 million people each year, and these infections cause hundreds of thousands of deaths. So you might be surprised to hear that CSIRO’s been releasing millions of mosquitoes along the Cassowary Coast in north Queensland. Even stranger, the locals have been helping out!

Our mosquito releases are actually a trial of anti-mosquito technology. And the mosquitoes we’re releasing are not as bad as most. We’re only releasing male mosquitoes, and males don’t bite. Instead, they drink nectar, fly around looking for a mate, and then die.

The males we’re releasing have been treated with a bacteria called Wolbachia, which is harmless for humans, but has a strange effect on these mosquitoes. When one of these male mosquitoes mates with a wild female, none of the eggs will hatch.

That’s the key to the project. If we can make sure the local females mate with these special males, then boom! No more ‘baby’ mosquitoes, which means in a few weeks’ time, no more adult mosquitoes. At this stage, there’s no way to get rid of all the local males. The best we can do is try to crowd them out.

It’s a mammoth task. We’ve been working with James Cook University and QIMR Berghofer to breed around 20 million mosquitoes.

Then we need to sort them so we release just the males. Luckily, a company named Verily has mosquito sorting technologies that make the task a lot easier.

The early results are promising. During the trial, the population of wild mosquitoes dropped by more than 80%. With some improvements, this technique might make pesky mozzies history!

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  1. As I see it one of two things may occur:
    1 Mosquitoes die out
    2. Mosquitoes evolve like sea horses and the males are able to change sex and become females to allow mating and you’ll never be able to get rid of them.
    You better hope it is “1”

    1. Hi John,
      Good thoughts! I think what might happen is sadly more boring that your Jurassic Park option – sorting through millions of mosquitoes, a few females might slip through, and they start a new population of mozzies immune to the program.

      Something similar may have happened before. While researching the story, I found out that the local mosquitoes are already infected with a similar bacteria, from a previous mosquito control test. Luckily, the two bacteria are incompatible with each other.

      Maybe the answer is to come up with hundreds of different bacteria, each incompatible with all the others, and then release a whole rainbow of different males out there. Females would have a hard time finding just the right mate, no matter what bacteria they carry!

  2. Doesn’t the fact that some of the previous test mozzies survived that bacteria suggest that over time a super mozzy will be immune from whatever you throw at it? The more different bacteria you try the hardier will be the survivors?
    I never liked the idea of living in bug infested NSW or Queensland anyway so I’ll be safe. Don’t like your chances though!

    1. I reckon even if if a control technique becomes less effective over time, it can still be useful – look at myxomatosis as an example. It’s still killing some rabbits, and combined with calici, we’ve avoided rabbit plagues like we got back in the late nineteenth and early twentieth centuries.

      I’ve got no idea whether mosquitoes adapt to this bacteria either – it’s not killing them, just making them selectively sterile. The bacteria probably profit from this, so at a guess it might end up in an arms race between mosquito adaptation and bacterial evolution.


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