Written by Jamie Baxley
After Hurricane Florence caused massive flooding across North Carolina in September 2018, several flooded areas were plagued by swarms of nickel-sized mosquitoes.
In addition to being larger than regular mosquitoes, this biting insect was also significantly more aggressive. They hatched all at once from eggs lying dormant in the soil. Some eggs lay dormant for as long as two years, only to be awakened by the Great Flood.
The outbreak made national news, but mosquitoes are a common nuisance in low-lying areas of the state during floods. Earlier this summer, Tropical Storm Debbie caused an outbreak of the insect in Brunswick and New Hanover counties.
Hurricane Helen could cause another hatch festival. Much of central and central North Carolina is at risk of “rapid flooding due to excessive rainfall” Friday, creating ideal conditions for flood mosquitoes, according to the latest forecast from the National Weather Service. .
Michael Reiskind ||Credit: North Carolina State University
Few people know more about this vampire breed than Michael Reiskind. Reiskind, a swamp-loving native of flood-prone Florida, wrote his master’s thesis on the spread of dengue fever, a mosquito-borne virus, in Peru. He is currently an associate professor of entomology at North Carolina State University, with several academic dissertation credits on mosquito ecology and biology.
Reiskind said flood mosquitoes generally “do not pose a significant threat to human health,” but their “huge numbers” can make going out uncomfortable, especially for people in rural areas.
Mr. Reiskind recently answered some of our burning and itchy questions about pests. His comments have been edited for length and clarity.
North Carolina Health News: What is a flood mosquito? How is it different from other types of mosquitoes?
Michael Reiskind: There are several characteristics of mosquitoes during floods, one of which is rapid development.
Most mosquitoes that we think of as flood mosquitoes have an egg stage that is resistant to desiccation and death. Their eggs can remain in the environment until a flood occurs, sometimes for years.
This creates a store of eggs waiting to be used, which can lead to large numbers of mosquitoes in a very short period of time after a flood.
NCHN: Can mosquitoes transmit diseases during floods?
Reiskind: One of the good things about flood mosquitoes is that we don’t typically associate them with human pathogens.
However, while they do not directly pose a major threat to human health, they can pose a threat to dogs. Some of these mosquito species are known to transmit heartworm disease to dogs, which can be extremely dangerous and even fatal.
Thankfully, this is a threat that can be controlled. You can prevent canine heartworm infection by visiting your veterinarian and having them prescribe preventive medication for your dog.
NCHN: Where in North Carolina are areas most likely to experience flood-induced mosquito outbreaks?
Reiskind: Coastal plains are places where the topography is not so rugged that water stays where it lands. Generally, these are the areas at greatest risk for mosquito outbreaks.
But anywhere in North Carolina, if we get a lot of rain, we’re going to see some increase in mosquito numbers. For example, the flatlands east of Raleigh can be in very bad conditions after heavy rain. It doesn’t have to be a hurricane. A large rainfall event could have the same effect on the region.
NCHN: How long does it take for mosquitoes to become active after a flood occurs?
Reiskind: Some of these flood species develop very quickly.
If it’s warm outside, it can develop within just four to five days after a major rain event or hurricane. It will then probably continue to develop for as long as the flood exists. Hurricane season can last several weeks.
If you’re lucky, a cold front may pass through and that could be your best mosquito control. It essentially freezes them.
That being said, cooler weather seems more and more distant these days.
NCHN: Are flood mosquitoes more aggressive than other mosquitoes, or do they bite more easily?
Reiskind: We cannot say with confidence that mosquitoes during floods are more aggressive than other species. It just hasn’t been studied.
However, if you read historical accounts of certain species of flood mosquitoes, you will find that they are definitely aggressive. Their adult lifespan is fairly short and they need blood to produce the next egg.
Almost all mosquitoes suck blood, so you need to find a way to do it. Do they sneak up and eat your ankles when you’re not looking? Or will they come straight at you and risk a whack to finish it off quickly?
NCHN: After a flood, what steps can people take to prevent or reduce the risk of mosquito bites from flooding?
Reiskind: It’s pretty unpredictable where hurricanes will hit. So when it comes to preventing mosquito outbreaks during floods, there aren’t many easy answers.
After the fact, it is possible to kill the adult insects and reduce their population through aerial spraying of insecticides. Consumer-grade repellents are also effective against flood mosquitoes, but I will say that I have never tested them in a situation where a million mosquitoes swarm.
Personal protection is one way. One example of this is wearing warm clothes, but being outside in a hot, humid environment after a hurricane probably isn’t very fun.
There are also backyard mosquito control solutions available through private companies. These typically work by applying an environmentally stable insecticide that attaches to the plant for about 21 days.
However, after a hurricane, aerial spray from large aircraft will not be as effective as directly attacking widespread mosquito populations, as heavy rains can essentially wash away the insecticide. .
NCHN: What role does climate change play in the frequency and intensity of mosquito outbreaks during floods?
Reiskind: One of the things that’s becoming pretty clear with climate change is that we’re seeing more intense storms.
It’s not always just hurricanes. We also see other weather systems occasionally producing hurricane-force amounts of rain.
I’m not a climate scientist, but I know that there is still a lot of research being done on precipitation events and building accurate models to predict future precipitation events under climate change scenarios. I am. However, I think most people agree that we will continue to see more intense rainfall events, which will definitely lead to an increase in mosquito populations.
NCHN: What are the biggest challenges in controlling mosquito populations during floods, especially in rural and hard-to-reach areas?
Reiskind: In rural communities, it’s all about the size of the area involved.
For large areas, there is no way to predict where flood mosquitoes will be abundant or where there will be very few mosquitoes. No science is available at this time.
I also think there’s probably some cost-benefit analysis that impacts rural areas. If we are talking about a very large rural area with a low population density, is it worth considering the economic cost and environmental impact to treat that area?
NCHN: Are there new technologies or methods being developed to better manage or predict flood mosquito outbreaks?
Reiskind: In the mosquito world, we are developing genetic methods to control mosquitoes.
However, flood mosquitoes are very difficult to deal with due to the nature of their biology. Generally, we don’t have the ability to study them in the lab. So it’s almost impossible to do something like genetically engineered mosquitoes with these species.
From time to time, new chemical approaches emerge. But let’s be honest: these approaches are usually not innovative.
My guess is that mosquitoes during floods will continue to be a problem for the foreseeable future. I don’t think there will be any major technological innovations that can be easily applied to post-flood situations.
At the same time, I am very impressed by the work that some of my colleagues who study geography and landscape are doing. There may be potential for highly customized control approaches, perhaps using detailed maps and statistical models to spray insecticides in areas that are likely to be hotspots for mosquito outbreaks. I don’t know.
But I think a significant amount of research is needed on how to build these models and deploy something like that. This is a solution that could still take a decade or more to implement, even if we started in earnest today.
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