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Where Do Mosquitoes Living in Cities and Towns Come From?

By Chris Williams on April 1, 2016.

John Maher: Hi, I’m John Maher and today I’m here with Tim Chase of Colonial Pest Control. Tim is an entomologist and a pest control technician and today our topic is where do mosquitoes living in cities and towns come from? Welcome, Tim.

Tim Chase: Good morning, John.

Are Different Species of Mosquitoes Living in Cities & Towns?

John: So Tim, are there different species of mosquitoes and are there different ones living in cities and towns? We live in Massachusetts, and [there are mosquitoes] throughout New England. How many different species of mosquitoes are there?

Tim: According to studies, there’s 51 known species in Massachusetts. Some are very common, like the salt marsh mosquito and some are less so, like some of the mosquitoes that feed on bird and reptiles. The might be found more commonly deep in swamps or high up in the canopy of trees. There’s quite a few different species that we run into. Most of the species that we see are known vectors of several diseases. Mosquitoes as you know, are very active disease vectors. What a disease vector is, is it’s actually an insect that’s going to have a blood meal from a host to lay its eggs. And when it does that, it actually picks up disease organisms, and then it can actively spread that to other animals that it feeds on during its feeding.

John: Right, so it picks up a disease from one animal and then goes and bites another animal and it transmits that disease.

Tim: Exactly. So, which species [you see] depends on the type of habitat that is present. Things like standing swamps versus moving water. A very clean river as opposed to a polluted river. Seasonal pools, drainage ditches, culverts, and things that remain wet and moist for over 6 weeks are perfect breeding habitats. Some mosquito species are present mostly in the spring, some are present in the late spring, and there are species that are more active in the early summer and then in the late summer and fall. So, depending on the habitat and conditions, different species are present at different times and at different levels.

Mosquito Populations During Different Seasons

John: Okay, so depending on where you live, you might have more mosquitoes and in the spring than in the fall, and in other places, you might have more in the fall than in the spring. Or, you might just have mosquitoes all the time. It’s one kind in the spring, it’s a different kind in the summer, it’s a different kind in the fall and it’s just constant.

Tim: It’s just constant. There are species that have several generations over the summer, so we could imagine that those species are going to sort of compound themselves as the season goes on. There are species that have a single generation, so they’re not as prone to be a mass. The female will emerge, she’ll get a couple blood meals, lay her eggs, and then the eggs will overwinter. So, that’s not such a prevalent problem, unlike the salt marsh mosquito who can have two to three generations per season. And those overlapping generations can just create huge amounts of mosquitoes. In that, there’s more potential for the spread of disease and more discomfort for the general human population.

Where Do Mosquitoes Living in Cities Come From?

John: Right. Let’s talk about cities a little bit. We think of cities as being places where you don’t encounter mosquitoes as often as you would if you’re in a rural area where your house might be right against the woods or something like that. But clearly there are mosquitoes living in cities, where do they come from?

Tim: Well, chiefly depending on the species, you’ve got a lot of water features in the Boston area. We’ve got the Charles River. Looking right at a little pond at our office here, and we can see that those areas are certainly prone to mosquito activity. There are mosquitoes that will live in just wet, gooey stuff. So you’ve got mosquitoes that live in tree holes, for example. There are mosquitoes that would love to live in a sewer drain system or just a water runoff culvert from the streets. So those places that hold standing water for three to four weeks are certainly potential breeding sites. In fact, one of the most common sites for testing for mosquitoes and the West Nile Virus and other diseases are those culverts. They will actively reach down and pull out mosquito larvae and test them in those areas and look for the different species that might be present and the potential for disease organisms within those larvae.

John: I’d imagine that you’d have certain times, like if it rains and you end up with a lot of water in the sewers, but then it doesn’t rain for a few weeks, after that, now you’ve got that water just sitting there and it’s not being washed out or rinsed out. That would be the kind of place mosquitoes would live.

Tim: Absolutely. So, the weather conditions play a huge role in mosquitoes. If we have a really wet season and there’s a lot of standing water, a lot of pools and drainage ditches that keep getting replenished, we’re going to have a lot more mosquitoes that respond to that. Conversely, if we had a season where there really wasn’t a lot of rain, maybe those culverts didn’t fill up at all and the little streams and ditches that are normally a couple inches deep are just dry. I think we actually had that this spring, where we had just less mosquitoes overall. I believe that the 2015 summer showed less mosquitoes than 2014.

John: Yeah, I think I noticed that at my own house. My kids weren’t getting bit as often and I was kind of wondering why that was the case, because I remember the previous year being pretty bad. So that would be one of the reasons why. The weather really plays a large role.

Tim: And different species respond in different ways. So, you can have a dry season and some of the forest species that are dependent on these little pools just don’t have a robust season. Where the salt marsh mosquitoes, all they depend on is a couple good high tides. So their breeding area is completely different and they’re unrelated to the rain as much as some of the other mosquitoes.

Mosquitoes Breeding in the City & Keeping Them Out of Your House

John: Right. We talked in a previous podcast about places inside the house where mosquitoes can breed. So I can imagine that in cities, that would be something to watch out for as well.

Tim: Absolutely. So when you’re living in more compact areas, you might have more potted plants, or buckets of things up on your patio, storage in weird places between the structures. I know in cities, there’s very little yard space, so you might have stuff stacked up or under tarps.

John: In alleyways between apartment buildings and things like that.

Tim: Imagine a trash can that hasn’t been emptied that is filled with water. A bucket of yard trimmings that is just sitting there, filled with water.

John: So that would be one thing you could to do help prevent mosquitoes in the city. Make sure you have all your trash cans have lids that don’t have holes in them, make sure you’re not leaving buckets out on your back porch or something like that.

Tim: Again, you’re just reducing breeding population sites and if you have less of those, it’s just going to make sense that you have less mosquitoes. All of the above, the same integrated pest management strategies that could be used for a residential neighborhood certainly expand out to more city type of things. Even though there’s more hardscape, there may be more actual underground drainage, so those are ideal breeding spots, which you might not have in a rural situation. So we certainly do have sewers in my town, but when I look down into it, they’re usually running or they’re pretty dry. There’s two conditions there. So you’re not going to have a lot of breeding in heavily running water, like you mentioned earlier. If the larvae all get washed away in a flood, there they go. That has also happened historically. You’ve had super wet weather, where it was just so wet that the larvae were washed down stream.

John: That’s interesting that in the dry weather, the mosquitoes might not have a place to breed and in the very wet weather, they might not have a place to breed either because that water is constantly being replenished and washed away.

Tim: So there’s a lot of stuff that goes into mosquito outbreaks, if you will. [It depends on] who’s actually in the area and what they’re doing. If you have a giant bird population, [you might see more mosquitoes]. I drive by Haverhill and there’s 10 million crows that go by over 495 every night. They all go somewhere, and they all are sitting together and the mosquitoes that feed on crows are there.

John: They know that.

Tim: So there’s a population. When the West Nile Virus first hit, one of the first things they were doing was monitoring dead crows.

John: That’s interesting.

Tim: And that seemed to be a population of animals that was sort of like a bellwether. All these dead crows, what’s happening? It’s the West Nile Virus. [The question was,] could it affect humans? Yes. There were multiple cases, but most of them weren’t fatal but there have been several deaths according to the studies. Apparently it affects birds in a much greater capacity for whatever reason.

Mosquito Species Across New England

John: Are there different mosquitoes that live in the northern part of New England versus the southern part of New England?

Tim: Definitely, mosquitoes have a range. Keep in mind that as the temperatures warm every year, we’re going to have more of these southern species sort of encroaching up into our area. So, we are seeing the Asian Tiger Mosquito. There’s a couple other mosquitoes that have been showing up in Connecticut. Very interesting. They weren’t in Connecticut about 10 years ago. Maybe people brought them in with them in some type of water item, but the most likely thing is that they’re just slowly coming north with the warmer weather.

John: Right, as it’s starting to warm up.

Tim: And as we head up into northern Maine, there’s going to be species that are probably not as prevalent in Massachusetts.

John: They’re more resistant to the cold weather up there. They can make it through the winter.

Tim: Yes, exactly. But geographically, we’re still sort of in the same area. There are species that range from southern Canada all the way to Mexico and halfway across the country where it changes a little bit. Some of these species are very, very widespread across North America and Europe. It’s just amazing how common some of these insects have become.

John: What are some of the ways that somebody living in a city or in a town, maybe a little bit outside of the city, can prevent mosquitoes from getting into their house?

Tim: One of the main things you can do is just make sure your house is sealed up tight. If mosquitoes can’t get in, they can’t get in. Again, reducing breeding sites around the structure. In some cases, if it’s really bad and you’re having a mosquito explosion, maybe keeping the lights off at night outside that attract mosquitoes. If your house is really a beacon for insects, they will come. So if it’s a really bad mosquito season, it might be one of your options. Another thing that might be considered would be to minimize your time outside during dusk and dawn, when the mosquitoes are most actively biting. If you’re going to be outside during those times, you might wear long sleeves, long pants. Insect repellent containing DEET is known to be an effective repellent for mosquitoes. There are some other, more organic methods too that have less effectiveness but that can be used.

Long Grass & Mosquitoes

John: Should people keep their grass cut shorter? Does long grass attract mosquitoes?

Tim: I wouldn’t say it attracts them as much. Mosquitoes don’t rest as much as we might think. But keeping shrubs and stuff pruned back [is important.] The less resting places you have on your property, the better it’s going to be for you. If you can picture two yards, one of them has a heavy tree canopy over it and lots of shrubs around the edges, then the neighbor has no trees and no shrubs, which one of those is probably going to have more mosquitoes? I’m going to say the darker, moist habitat. That’s going to be more favorable for the mosquitoes. They’re really prone to desiccation. Mosquitoes are very tiny little insects, and the wind can dry them out very simply. So their mission is to get to a nice, kind of humid spot where there’s high humidity, not a lot of light hitting them because they don’t want to get hot, and they just kind of wait for a host to come by. They’re pretty much resting most of the time until a host comes by and they begin their active feeding cycle, primarily at dawn and dusk. That being said, depending on the species, if you walk out under the bush and it’s a day biter and she’s looking for food, she’s going to begin her feeding activities the second she’s stimulated by you.

John: Right.

Tim: That stimulation can include movement, shadows, CO2 and heat, and all of the above. So the mosquito is very adept at finding a blood meal and it’s mandatory that it does. These ladies are very hungry. Male mosquitoes don’t bite as it turns out.

John: That’s interesting.

Tim: The male mosquito is simply a mating tool. He’s got large antennae that are designed primarily to locate females. So they’ll eat a little bit of plant sap or some honeydew, or a couple various things. But they really don’t do a lot more than mate. So it’s the female mosquitoes we want to focus on.

John: Alright, well that’s really great information Tim, thanks for speaking with me today.

Tim: It’s been a pleasure John, thank you.

John: And for more information, you can visit the Colonial Pest Control website at colonialpest.com, or call 1-800-525-8084.

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