Q&A: Victoria’s monster mosquito outbreak

It’s evening and you’re just starting to relax after a busy day. As you do, you hear the unmistakable high-pitched whine of a circling mosquito. It’s something most of us are used to in Australia, but do you feel like it’s happening more often this spring? Or that there are more of those bloodsuckers hunting for food around?

We asked three experts from the University of Melbourne – PhD candidate Véronique Paris, Nick Bell and Professor Ari Hoffman from the Faculty of Science’s Pest and Environmental Adaptation Research Group – to explain exactly what happened.

The team noticed more mozzies when field training around regional and rural Victoria. Image: Shutterstock

Q) Are there really more mozzies this spring or are we just paying more attention to them?

Yes, there are more mosquitoes around this year than you would imagine. This is something we have observed ourselves

As part of our research, we conduct surveillance around our lab space and offices to check for mosquitoes that may contaminate our research colonies, and more have been recorded this year.

Since we run a lab where we breed mosquitoes for research, it’s important to make sure they don’t escape. All of the mosquitoes around our offices have been identified as Culex species, which we do not currently have in our research insectarium, which tells us that they are invaders, not escapers.

Obviously, since our friends and family know we’re researching mosquitoes, we get a lot of messages and calls about the increase in mosquitoes they’re seeing. And of course, everyone wants advice on how to control them.

As our team does a lot of work in the field around regional and rural Victoria, we’ve also seen this at our field sites.

But it’s not just Victoria where we’re seeing more mozzies – New South Wales is seeing an increase in explosive mosquito populations, and local experts expect it’s far from over.

Looking down the hallway in our building, we found about 20 mosquitoes hanging around the entrance – circled in red so you can see them. Image: provided

Given that we know these mosquitoes did not come from our labs, we are doing some genetic screening to determine what species these mosquitoes belong to. Interestingly, we suspect they are not human-biting species, as the team noted that they did not try to feed us when we were in the building.

Q) Why are there more mosquitoes this year?

Torrential downpours in southeastern Australia could be a big factor.

All mosquitoes need water to complete their life cycle, with some species specializing in breeding in very small containers such as old tires, discarded plastic containers and tree holes. Other species prefer larger bodies of water such as tanks or ponds.

Many pest mosquitoes breed well in standing water rather than flowing water, and recent rains and floods have produced more standing water.

This often includes new “mystery breeding sites”—under houses, garages, and places that may be harder to access than the bits and pieces of trash many of us allow to pile up around the yard—cleaning it up will mean you do. Your role in reducing the mozzie population.

Most mosquito species thrive in warmer conditions, so the combination of heavy rains and rising temperatures as we approach summer creates ideal conditions for mozzies populations to grow.

When examining field objects, we find many “wrinkles” in places like this ornamental pond. Image: provided

Q) Mosquitoes seem bigger, should we be concerned?

Mosquitoes range in size from very small to quite large.

There are over 300 species found in Australia and about 10 species are quite common around Melbourne. People all over the world mistake crane flies for very large mosquitoes, when in fact they are mosquito predators (commonly known as “Mosquito Hawks” in other countries).

These are good insects that won’t bite you and you want to have around your home. Spiders are also your friends – if you are comfortable with having spiders around your home, they will definitely help.

Then you have chironomids, which to the untrained eye look a lot like mosquitoes, but aren’t that closely related. Their common name – non-biting midge – is a little clue as to why there is no need to worry about them. Chironomids, like mosquitoes, breed in stagnant water and can form huge mating swarms.

Likes some ‘giant’ mosquitoes Toxorhynchites speciosusDo not bite people, which can be more than 12 millimeters in size. In fact, as adults, they are strictly vegetarian. Even better, their larvae (wrigglers) are predators, eating other mosquito larvae, so they’re another natural ally in your fight against mosquitoes.

Some “giant” mosquitoes, such as Toxorhynchites speciosus, do not bite humans. Image: Wikipedia

So, in general, the size of the mosquito should not worry you. Although many mosquito species do not bite humans at all, it is best to avoid them wherever possible.

Q) What can we do about them?

The most effective strategies are quite simple – avoid being outdoors at dusk and dawn, when human-biting species are most active.

Wear long-sleeved shirts and long pants. Make sure you use mosquito repellent if you’re outdoors, and don’t forget to reapply if you’ve exercised, gone swimming, or been wearing it for a few hours.

Do your best to get rid of potential breeding grounds on your property – anything that can hold permanent water.

Some mozzies, like a common pest Aedes notoscriptusit will happily breed in very little water, so drip trays under your plants are also a potential breeding ground.

This species can transmit viruses such as Ross River Virus and is also a prime suspect involved in the transmission of the bacterium that causes Buruli ulcer.

To ensure that mosquitoes don’t breed in your garden, remove trash from your property, such as old containers, tires and buckets, and empty all containers (such as drip trays under potted plants) after it rains.

Here are over 100 Aedes notoscriptus (Australian backyard mosquitoes) we collected in one hour last weekend. Image: provided

Also be sure to keep your faucets clean and make sure the pipes and screens around your water tanks are intact, repairing or replacing them if they are not.

Anything that can hold water is a potential breeding ground, so if you have a water reservoir, make sure mosquitoes can’t get in and lay eggs. Old septic tanks are also a common breeding ground, so if you live in the country or outside, make sure these are properly filled.

You can also buy granular products (“bug growth regulators”) to add to standing water that doesn’t drain easily.

With climate change introducing more variable conditions, including periods of more intense rainfall, it is inevitable that the frequency of mosquito problem periods will increase.

And areas that previously didn’t have as many mosquitoes could see explosive events like we’re seeing now.

Moreover, changes in the distribution of vectors and hosts of disease-carrying mosquitoes mean that diseases are emerging in new areas. We have already seen Japanese Encephalitis (JEV) acquired by migrating waterfowl in Australia.

Culex annulirostris It is one of the mosquito species that can transmit JEV. This species can breed in urban areas, but also in natural habitats, including scrub and wetlands.

It’s hard to pin down the exact spectrum of impacts we can expect from climate change, but we do have some examples of mosquito species shifting their ranges in response to climate change.

Mosquito larvae ‘wrigglers’. The rounder-looking pupae are the last stage of aquatic life before they become adults. This 200 millimeter dish contains hundreds of larvae. GIF: provided

A prime example of this is the Tiger mosquito (Aedes albopictus), Recently, its habitat has moved from being exclusively tropical and subtropical to now occupying much of Europe under warm conditions, and species are evolving to handle colder conditions.

Tiger mosquitoes are now found in the Torres Strait, but have not yet established themselves on the Australian mainland.

So yes, parts of Australia are seeing an increase in mosquito numbers this spring, and we’ll see more springs like this when the real effects of climate change kick in.

Banner: Shutterstock

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