Jordan
It’s time to rejoice, fellow Canadians, we have survived another winter. Everywhere in this beautiful country of ours, the temperatures are rising, the sun is shining. We did it. All that remains now is to dust off our porch chairs, unlock the cottage, pull out the patio furniture, relax and bask in the glorious spring weather. And summer is coming. So what could possibly spoil that? Right, those f****** things. Mosquitoes, the scourge of Canadian summers. And most of the methods that we have to control them involve pesticides, which aren’t great. So it’s worth asking, is there another way, a better way to keep these incredibly annoying creatures under control? Oh, and also, when I say under control, does it have to mean keep to a reasonable, minimally annoying level, or can we just try to exterminate them? Do we really need mosquitoes anyway?
I’m Jordan Heath-Rawlings, this is The Big Story. Sean Prager is an assistant professor at the University of Saskatchewan where he researches insect ecology. Hi, Sean.
Sean Prager
Hello. How are you doing?
Jordan
I’m doing all right. I’m not looking forward to mosquito season.
Sean Prager
Most people aren’t, although mosquito season does bring other pleasant things.
Jordan
That’s true. And we’re going to talk mostly today about mosquitoes in big cities and specifically a new project in Edmonton. But maybe just to start, in regards to mosquitoes and cities in general, how big a problem can they be to big cities if they’re not controlled in one way or another?
Sean Prager
It depends on the city. Geography is the big driver in many ways of whether or not you have problems with mosquitoes, because on their own, mosquitoes are not anything more than annoying. The reason a mosquito is a problem is because it’s the vector of diseases. And that really then depends on are you in a city, in a location in which there’s a disease about which you need to be concerned. In some cities, more so than others.
Jordan
Well, speaking of that then, from here, where I am in Toronto, I remember probably more than a decade ago now for several consecutive summers, West Nile was huge news and a real concern. What happened to West Nile? Did it leave our area? Did it go somewhere else? Did we figure out how to control it? It just doesn’t seem to… obviously, the last couple of years, there’s been more important virus to talk about, but it seems to be largely relegated to the background in terms of mosquito borne risks.
Sean Prager
It’s endemic now. When you’re thinking of and probably this would be say around when I started graduate school, when I first showed up, it was a new problem and it was only sort of recently found. And you were finding people that were sick and people still get sick with some frequency. I mean, it’s not unheard of, but we now have better ways of monitoring it. We understand what it does and we have more established ways of managing it or mosquitoes. And we know to the extent to which we have to do so. So it’s still there. Every year in Ontario, there are cases of West Nile in birds and horses and people. It’s just that we don’t make so much of a big deal about it.
Jordan
You kind of equated two things there. When we talk about managing West Nile, are we really talking about managing mosquitoes or are there other aspects to it?
Sean Prager
When you manage a vector born disease, with few exceptions, you’re always managing a vector. And in fact, that applies to really sort of any vector borne disease, whether it be something that affects humans or livestock or plants. There’s very few examples to date where you can do it otherwise. And so you’re always managing mosquito.
Jordan
So how would a big city like Edmonton or Toronto typically, before we get to the interesting program we’re going to talk about, typically control its mosquito population? What has been the standard for that?
Sean Prager
Once upon a time, the standard was to drive around with a truck spraying DDT, but that’s obviously been transitioned to driving around in trucks spraying other pesticides, and then now really to do none of that. So especially for things where we have a more developed understanding of what to do, we have tiered approaches. A lot of it involves the use of larvicides and monitoring. So a lot of it is monitoring. So you can assess the relative risks of what you have. So are the mosquitoes in pools or birds or whatever transmitting a particular disease you have to worry about? And then a lot of it’s cultural control and encouraging people to not keep water standing and all those sorts of things. And then we use larvicides, so we have different kinds of relatively soft materials, sort of BT toxins that we can put into water and stuff to kill the larvae of mosquitoes.
And then it tends to ramp up from there, where there are often or occasionally aerial applications of insecticides with helicopters and airplanes and things like that. But that’s usually only if you have a real problem. And in fact, that’s why you see that more commonly in places like Texas or something where you have other mosquito problems. But it’s an array of tools, a lot of which starts with relatively sort of active monitoring and low level preventative things.
Jordan
So from DDT to pesticides to now, what sounds like some insecticides but much more targeted, what have we learned about trying to control these populations through spraying, whether that’s from a truck or targeted from a helicopter?
Sean Prager
I think we know that you can do it. I mean, it depends on the material. So DDT was very effective for killing mosquitoes. It just isn’t particularly good for other reasons. We’ve moved on to other things and insects, especially mosquitoes, they develop resistance. And so we know that there’s consequences of using these things. And it’s not always optimal and it’s not that precise and it can work, but it’s not the most effective thing. It’s a last resort when you’re sort of desperate, I think in many cases.
Jordan
So tell me what’s happened in Edmonton then to change their approach. And as somebody who studies this, why it interests you.
Sean Prager
What happened in Edmonton is that there seems to be a bit of a conflict where people have decided that the traditional approach that they had been using of sort of aerial applications of insecticides is maybe undesirable and that they want to move to things that are less crude, less use of insecticides, less spraying countryside to try to limit mosquito populations and perhaps less extreme, I guess, in some ways. And so I guess the city Council and various people have pushed towards a more holistic approach to managing their mosquitoes.
Jordan
What does that holistic approach look like?
Sean Prager
Well, it’s funny. I would say it looks like doing what a lot of ecologists and insect management people would say you should do anyway. In other things, we would refer to it as integrated pest management, using the tools available to you, particularly sort of ecological tools to reduce those insects that you don’t want, to remove pests. And so it looks like using a whole array of tools rather than relying on insecticides. And really, this is the approach that people have been taking in, say, agriculture, or at least been pushing for 40 or 50 years. It’s just a little bit less effective, sometimes they’re less likely to be adopted in sort of control of urban animal medical pests.
Jordan
Explain a little bit more about how you can landscape or design public areas, urban areas, wildlife areas to help control a population of mosquitoes.
Sean Prager
So it starts with the biology of a mosquito. And it’s worth noting that when we say a mosquito, there’s numerous mosquito species. So in North America, there’s maybe 170-ish, I can’t remember the exact number, far fewer necessarily in Alberta. But there are many species. So it’s worth starting to say while we say mosquito, we actually need many species of mosquito. Of those, of course, only several are ones that we particularly care about because many of them don’t bite people. And ultimately it’s things that by people that tend to be what we are interested in.
Having established that, nearly every mosquito species lays their eggs in or around water and they basically all have an aquatic nymphal stage, that is as juveniles, so if you think back to your basic entomology, if you remember from, say, grade school, you have an egg and in this case you have a larvae, larvae sort of like Caterpillar. But in this case, the larvae is sort of an aquatic thing that has a little siphon that sits at the top of the water typically, and then they eventually emerge as an adult and the female adults go around biting people to get blood, which is a source of protein for them.
So what that means is that if you have water of the appropriate quality for a given species that might be standing water, running water, mucky water depends on the particular insects, what they like. But basically, if you have water, that’s what they like. And in many of the urban mosquito species, what they want is sort of standing water like we have in pools and ponds and bird baths and things. Well, if you have that water, then you have a good place for these insects to lay their eggs. Landscape so you have less of that water around, or so it moves in different ways. That alone reduces the breeding places for those insects.
But then on top of that, there are many things that are aquatic predators. And so if you have things where not only is that water not standing quite the same way where these mosquitoes will come around and later eggs and develop, but also where there are things that will be eating those larvae of the mosquitoes, then you’ll also reduce those numbers before they get out to be sort of adults. That’s the basic premise. And then within that, you can manipulate all sorts of things to make them move more easily or not as far or to induce them to lay their eggs in places that are far away from people and all those sorts of things.
Jordan
What about the animals that Edmonton is trying to encourage, I guess, is maybe the best way to put it. What are they using and how are they expected to help?
Sean Prager
So mosquitoes in both their juvenile and their adult forms are food for a lot of things. And of course, the one that we don’t think about or maybe we do think about a lot, of course, bats. So bats consume enormous amounts of insects in different cases, and mosquitoes in some cases are one of those. And so a great way of managing mosquitoes is to encourage bats, because bats are excellent predators, or at least those species that eat mosquitoes. And so if you have more bats, you have more things eating mosquitoes, and they will do that on their own. So you just need to sort of make more baths, which of course, we do, by adding sort of bat habitat, bat houses, bat boxes. And those bats will go around at night and they will eat all those mosquitoes and they will happily do it. And it’s better for the bats, which are kind of nice to have around anyway, and reduce the mosquito population. That’s one thing you can do. And there are some birds or other species that also will eat mosquitoes.
And then there are, of course, fish species that will eat the aquatic larvae of the mosquitoes, and there are other insect species that will eat the aquatic larvae of those mosquitoes, including actually, Interestingly enough, other mosquito species whose larvae will eat the larvae of other species. And so all of those things will go around and they won’t just reduce the populations. They’ll keep fewer insects around to begin with, and they’ll do it just by going across their sort of natural lifecycles.
Jordan
Specifically bats and I guess dragonflies, if you’re the city, how do you make sure that these creatures, I guess, end up where they’re needed and that they seek out the right prey? This sounds like a stupid question, as I say it, but how do you know that that’s actually going to happen?
Sean Prager
Well, it gets to the individual biology of the individual organisms. Bats are probably a little bit straightforward. You place bat boxes in those places that are near where the mosquitoes are likely to be or where you want them to remove the mosquitoes. And so the bats are going to live in the bat boxes and they’re going to go out looking for food. And like many things, if there’s a lot of food sources nearby, the odds are at least in theory that they’re going to eat those mosquitoes nearby because why would you fly farther to find them? So that’s the simplest thing. You add bat boxes in the places that you want to either not have mosquitoes or where you think that the mosquitoes will be in, and the bats will consume them. So that one is, in some ways at least theoretically straightforward.
The Dragonfly is a little more complicated. Dragonflies are also an organism that has a sort of metamorphosis where their adults are flying predators. And so they eat things which they kind of pick off from the water. And their juveniles, so their larval stage is very voracious as an aquatic predator. So if you add those into the water because they are not going to move out of the water until they are adults, if you pick the right species, those that you know to consume mosquito larvae, and you put them into the water where you want, and you make sure that those conditions in the water are suitable for those juveniles. So not polluted, not too saline, whatever it is that they like. Well then those larvae should go around in the water eating the mosquito larvae because they need food. It gets a little more complicated as adults, the adults can fly pretty well, and so it’s possible that they would move to other locations. But similarly, if you have food sources, you’re going to probably stick to where the food sources are. Ultimately, that’s what a lot of it comes down to, making sure that you sort of add them and then keep the conditions that they like so that they stay put basically.
Jordan
How do we know that this kind of environmental intervention won’t backfire and the city of Edmonton gets to control the mosquitoes a little bit better, and then three, four, five years down the road, everybody is at city Council complaining about the overpopulation of bats and dragonflies in their backyards?
Sean Prager
How do we know that? Well, the good thing is that this is a little different than, say, cane toads in Australia, they’re suggesting the placement of things that are already generally native to the area. And so we know this, or at least we can make a pretty good guess based on our fairly in depth understanding of population biology. I mean, that’s ultimately what it comes down to, particularly aquatic ecology. People have been studying things like Dragonfly larvae for decades, and so we have a fairly good idea of how they act on some pretty specific levels.
And so there are things that would naturally be expected to be found in water. So in most places in which you have aquatic environments, we expect these organisms to be here. This is something that we know. And so we’re not adding things that are unusual, and therefore, we expect them to follow the sort of basic dynamics, which is that if the population of mosquitoes goes down, then the population of predators will follow, because that is what ecological theory and many, many, many hundreds of studies have shown happens, which is that if the number of prey go down, the number of predators will go down with it. And so we shouldn’t have overpopulation of these organisms, because they’re not invasive, because they’re going to follow what we would expect to happen.
Jordan
Speaking of the numbers of prey going down, is the goal here, and I’m sure, well, I know I would love it, I’m sure lots of people would, to eliminate all mosquitoes in the city? I know Alberta has a whole thing with rats in that manner, but I guess my question is just, do we actually need mosquitoes? I know everybody hates them. What role do they play in the ecosystem?
Sean Prager
This is a really sort of a complicated question in a way, and it has several layers. If we step out from Alberta and we just look at mosquitoes in general, people have thought about this a lot, and people have thought about this a lot, partly because, again, while in our regions, mosquitoes are mostly annoying, that’s primarily why we don’t like them. Obviously, in other places, they are substantially more problematic than being annoying. Of course, in parts of South America and certainly parts of Africa and Southeast Asia places with malaria and dengue, they’re responsible for more deaths than any other animal. And so in those cases, there’s a different equation. People want to eradicate them or at least certain species because you want to get rid of the risk of malaria and dengue.
What we seem to believe is that they do serve a role in the ecosystem, and in some of those cases, it may not be that dramatic. So people have thought about different species, and in many cases, if you remove them completely, we would guess that other things would fill their niches, but it’s hard to know. And it’s probably specific to each environment. All those things that we just talked about that eat mosquitoes? Well, if you take away all the mosquitoes, they have nothing to eat, and so that’s a problem. They may turn to eating other things or they may themselves not have anything to eat, and that’s not necessarily desirable.
Some mosquitoes are pollinators. People don’t think about it that way. But adult mosquitoes, even the females, when they’re not eating bloody, eat nectar from different plants. And so they are the pollinators of certain things, although as far as I know, certainly not in North America is there anything that’s exclusively pollinated. And so, like lots of things, they have an ecological role. They serve purposes in some way or another, or at least they have a role in the environment. If you remove them, you get whatever happens when you remove something. And it’s a little bit difficult to predict, but the general belief is that the world wouldn’t come to a screeching halt. Like it wouldn’t be environmental devastation if they were all gone. But in most places, at least in most places in Canada, they’re not causing the kinds of trouble where I think it’s warranted to try to eradicate them. I’m not sure if that quite answered your question.
Jordan
It does. And I’m honestly kind of fascinated by how you must feel as somebody who studies them, when a jerk like me or anybody else is like, can we just kill all these things? They’re super annoying. Does that make you mad?
Sean Prager
No. Because someone who thinks about mosquitoes, even part time, like I do, you come to it for different reasons. And again, I think that they’re annoying and people don’t like being annoyed and they make you uncomfortable. But also I do think that many people understand that they are the cause of some severe illnesses in places. And so even those of us who think about mosquitoes carefully from, say, an ecological perspective or from other perspectives, we are thinking about how you can get rid of them. But I think often we think about it realizing that most places we want to get rid of them, we want to drive the numbers down to the point where they’re not going to be problematic for people. But really what we want to do is it’s a public health issue, I think in most cases. So that’s why there’s millions, perhaps billions of dollars at this point spent on considering different ways of managing mosquitoes, because in many places they are a real problem, and you would want to eradicate them.
And I think that’s the other half of this, of course, is that there is a certain thing of an ethical decision at this time. What is the value of the risk of environmental damage or things you don’t like or whatever considerations you have relative to the perceived benefits of getting rid of the mosquitoes. And I think if you were in some places, they would say it’s a no brainer that half a million people to a million people die of malaria. And so probably getting rid of the mosquitoes is worth it to save a million people a year. But to not have mosquitoes bite you when you’re on your back porch in Muskoka is maybe not the same thing.
Jordan
That leads me to my last question. I really appreciate that answer. I’m just always fascinated by folks who spend such a great deal of time studying creatures that other people don’t, frankly, like. But my last question, which is probably just a practical one for anyone who’s listened this far. You mentioned standing water as something the city can do. What can people themselves with backyards, Muskoka cottages, you mentioned porches etcetera, do to keep their own hyper local mosquito populations under control?
Sean Prager
Same thing. Same thing. You can get rid of standing water. You can go and buy larvicidal disks they call Bacillus Thuringiensis Israelensis. It’s sort of a bacterial derived toxin. So it’s essentially a kind of biological control and you can throw them in the water. It’s just like what the cities do, and it will kill the larvae of the mosquitoes. And it’s fairly specific, so it shouldn’t bother anything else. So obviously those things you can do to keep the mosquito numbers down, you can try not to let your bird bath sit around, you can have the water move, all of those things, obviously.
And then if you’re really concerned about being harassed by mosquitoes, you can sort of take kind of personal preventative actions. Deet works extraordinarily well, and it has for decades, and we know this. So if you’re particularly concerned about being bit by mosquitoes, you can use Deet. And there are several other now alternative compounds we also know work nearly as well that are also repellent. Those are good options. We now can in Canada buy at least some clothing that’s been impregnated with compounds to make them anti-insect, anti-mosquito. So you can wear those.
Jordan
Oh, that’s cool.
Sean Prager
Yeah. So that’s really cool. So you can do that and you can walk around for hours and the mosquitoes probably will never come near you. They have a pyrethroid insecticide impregnated into them, so it’s kind of harmless to people, but the mosquitoes really dislike it. And then some of those things that you can buy off the shelf do work. And again, often they have these pyrethroid insecticides in them. So things like those Off lanterns, they work and they work pretty well. And if all you want to do is sit outside for a few hours and not have the mosquitoes bite you, that’s a perfectly reasonable approach to keeping them away from you for a while. And they’re relatively limited damage because mostly they just repel the insects and then it goes away when you stop burning it.
Jordan
Can I get a bat box? It sounds cool.
Sean Prager
You can get a bat box. Yeah. There’s several organizations that will help you out with them locally in different places and there’s also instructions online usually for making bat boxes. They’re pretty straightforward and they’re cool. Yeah, they’re really neat.
Jordan
That’s amazing. Thank you for all these tips. Thank you again for walking us through this and here’s to a relatively mosquito free summer.
Sean Prager
Thank you. You’re very welcome.
Jordan
Sean Prager of the University of Saskatchewan. That was The Big story. For more head to thebigstorypodcast.ca find us on Twitter at @TheBigStoryFPN. Write to us, the email is hello@thebigstorypodcast.ca [click here!].
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Thanks for listening. I’m Jordan Heath-Rawlings. We’ll talk tomorrow.
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