Q&A: The Monster Mosquito Explosion in Victoria


It’s evening and you’re just beginning to relax after a hectic day. Just as you do, you hear the unmistakable moan of a mosquito circling. 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 these bloodsuckers looking for a meal?

We asked three University of Melbourne experts – PhD student Véronique Paris, Nick Bell and Professor Ary Hoffmann from the Faculty of Science’s Pests and Environmental Adaptation Research Group to explain exactly what’s going on. .

The team noticed more mozzies as they worked in the field around regional and rural Victoria. Photo: Shutterstock

Q) Are there actually more mozzies this spring or are we just noticing them more?

Yes, there seem to be more mosquitoes this year, you can imagine. It’s something we noticed 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 we have recorded many more this year.

Because we run a lab where we breed mosquitoes for research, it’s important to make sure they’re not escapees. All mosquitoes around our offices have been identified as Culex species, which we do not currently keep in our research insectary, which tells us that they are not escapees but invaders.

Obviously, because our friends and family know we are looking for mosquitoes, we get a lot of messages and calls about the upsurge they are noticing in mosquitoes. And of course, everyone wants advice on how to control them.

As our team works extensively in the field around regional and rural Victoria, this is something we have noticed in our field sites as well.

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

When we looked around a hallway in our building, we found about 20 mosquitoes hanging around the entrance – we’ve circled them in red so you can spot them. Image: Provided

Since we know these mozzies did not come from our labs, we perform genetic screening to determine what species these mosquitoes belong to. Interestingly, we suspect these are not a human-biting species as the team noted that they do not attempt to feed on us when we are in the building.

Q) Why are there more mosquitoes this year?

Heavy rains in southeastern Australia are likely to be a major factor.

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

Many nuisance mosquitoes breed well in standing water rather than running water, and recent rains and floods have produced a lot more standing water.

This often includes new “cryptic breeding sites” – places that can be harder to get to like under houses, in garages, and in the debris that many of us let accumulate around our backyards. yard – cleaning it up means you’re doing your part in keeping the mozzie population down.

Most mosquito species grow rapidly in warmer conditions, so the combination of heavy rains and rising temperatures as summer approaches provide mozzies with the perfect conditions for their populations to explode.

We find loads of “wrigglers” in places like this ornamental pond when we’re in the field inspecting properties. Image: Provided

Q) Mosquitoes seem bigger, should we be worried?

Mosquitoes vary in size from very small to quite large.

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

These are good bugs that won’t bite you and that you want to have around your house. Spiders are your friend too – if you’re comfortable having spiders in your home, they’ll 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 – the non-biting midge – is a clue as to why you don’t have to worry about them. Chironomids, like mosquitoes, breed in standing water and can form huge mating swarms.

Some “giant” mosquitoes like Toxorhynchites speciosus, which can reach more than 12 millimeters in size, does not bite humans. In fact, as adults, they are strictly vegetarians. Even better, their larvae (wrigglers) are predatory, eating other mosquito larvae, so they are another natural ally in your fight against mosquitoes.

Some “giant” mosquitoes like Toxorhynchites speciosus do not bite humans. Image: Wikipedia

So, in general, the size of a mosquito shouldn’t worry you. Although many species of mosquitoes don’t bite humans at all, it’s always best to avoid them wherever you can, just in case.

Q) What can we do about them?

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

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

On your property, do your best to get rid of potential breeding sites – anything can have standing water.

Some mozzies, like the common pest Aedes notoscriptuswill happily breed in very small amounts of water, so even drip pans under your plants are a potential breeding site.

This species can transmit viruses such as the Ross River virus and is also the main suspect involved in the transmission of the bacterium responsible for Buruli ulcer.

To make sure you avoid mosquito breeding in your garden, remove all rubbish on your property such as old tin cans, tires and buckets and empty all containers (such as drip trays under potted plants ) after the rain.

Here are over 100 Aedes notoscriptus (the Australian backyard mosquito) we collected in an hour last weekend. Image: Provided

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

Anything that can hold water is a potential breeding site, so if you have a water tank, 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 countryside or on the outskirts, make sure these are properly filled.

You can also buy granulated products (“insect growth regulators”) to add to standing water that cannot be easily drained.

With climate change presenting more variable conditions, including more intense periods of rain, it is inevitable that periods when mosquitoes become problematic will increase in frequency.

And areas that haven’t seen so many mosquitoes before could see explosive events like we’re seeing now.

Additionally, changes in the distribution of mosquito vectors and disease-carrying hosts mean that diseases are likely to appear in new areas. We have already seen the recent outbreak of Japanese encephalitis (JEV) in Australia, which was likely purchased by migrating waterfowl.

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

It is difficult to dissect precisely the range of impacts we can expect from climate change, but we do have a few examples of mosquito species changing their range in ways consistent with climate change.

Mosquito larvae ‘wrigglers’. Rounder pupae are the last stage of aquatic life before turning into adults. There are hundreds of larvae in this 200 millimeter container. GIF: provided

A key example of this is the tiger mosquito (Aedes albopictus), which recently shifted its range exclusively from the tropics and subtropics to have now invaded most of Europe as conditions warm and the species appears to be evolving to handle cooler conditions.

Tiger mosquitoes are currently 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’re likely to see more springs like this as the real impacts of climate change kick in.

Banner: Shutterstock


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