Most pest control professionals start their search for mosquito breeding grounds on the water’s surface, but sometimes these pests are reproducing in less conspicuous containers, making them even more challenging to control.
Container mosquitoes, namely the yellow fever (Aedes aegypti) and Asian tiger mosquitoes, lay their eggs along the water line of containers. This seems simple enough, until you realize that anything that holds water is a suitable container, including the grooves of plastic gutter extenders, the curves of old tires and even a water glass left outside for one day too long.
In a big backyard, all of these containers can be tricky to identify by humans, but mosquitoes don’t have any trouble finding them. Container mosquitoes lay their eggs along the water line inside of these unconventional containers, and the eggs exist in a dry, suspended state for as long as a year. But, as soon as irrigation or rainwater raises the water level just enough to come in contact with the eggs, they hatch.
Once the aquatic stage is complete, the adults don’t fly far from their larval habitats, because they have food sources and a place to lay their own eggs right there.
Fortunately, Dr. Roxanne Connelly, chief entomologist, Centers for Disease Control and Prevention, Fort Collins, Colo., has five simple steps to help PMPs — and their customers — clean out pesky container mosquitoes.
Step 1: Education
When people get a mosquito bite, they know it, but that doesn’t mean they know how to identify where mosquitoes could possibly be breeding, or know how to clean out those containers.
That’s why Connelly said that education is the first step a pest control professional can take in controlling container mosquitoes.
“A lot of people don’t realize that they have things in their yard that are creating nice habitats for mosquitoes,” said Connelly. “Show people where mosquitoes occur around their homes and show people how to get rid of them.”
She suggested volunteering to speak at homeowners’ association meetings, educating neighbors and making visits to community and church groups. Even a trip to the dog park can turn into an educational opportunity, especially when dog owners hear that these specific breeds of mosquitoes transmit heartworm!
Connelly recommends carrying informational flyers in your vehicle that feature pictures of those containers common in yards that may be hiding container-breeding mosquito eggs.
“The more you can talk about it, and the more you can make people aware of this and show them things they can do, the more we’re going to be able to get ahead of some of these container mosquitoes and hopefully prevent some of these mosquito-borne diseases,” Connelly said.
Step 2: Source Reduction
“Source reduction is the key to getting rid of these mosquitoes,” said Connelly. “And when I say remove the source, it should be clear by now what the source is, the source of these mosquitoes are these items that hold water and can support mosquito life.”
She suggests starting by organizing a neighborhood or community clean-up day where residents rid their yards of potential mosquito environments.
“There’s a limit to that,” she said. “Once you get rid of all the cups or bowls or anything that is in the yard that can come out, you’re still going to have some containers that people want to leave in place. If possible, modify those containers.”
For example, for gardens with rain barrel irrigation programs, there should always be a tightly screwed on lid or at least insect screen coverings. Insect screens also help control pests when placed at the end of gutter extensions.
“Because they’re corrugated, they have those little ribs in them and they’re laying flat on the ground, they hold water in those little areas, so even after the rain washes through there you have water that’s left behind and the container mosquitoes love to fly up in these and lay their eggs,” Connelly said. “One of the best things you can do here is lift the pipe and dump out the water on a weekly basis.”
Bird baths should be dumped and scrubbed with steel wool or a stiff brush weekly and any old tires should be disposed of properly. The Asian tiger mosquito was actually unintentionally introduced to the United States through shipments of used tires that also toted the mosquito eggs.
“If you’re doing an inspection of someone’s home, trying to look for the source, don’t forget to look above — look at the roof line,” said Connelly. Clogged gutters make a perfect habitat for container mosquito eggs just waiting for the next big rain.
Even tarps or litter as insubstantial as a bottle cap can support container mosquito eggs, said Connelly. “If it’s holding water, and it’s sitting there long enough, it can produce these container mosquitoes,” she said.
Plants, including the popular bromeliad plants native to south Florida, can house container mosquitoes in the water-holding tanks in their leaf axils.
“Don’t forget to look at the plants because while people may not think of them as a container, the mosquitoes sure do,” Connelly said. “When people plant these around their yard and they start having mosquito problems, we try to encourage people to go ahead and treat them.”
Holes in trees can become a natural container when the conditions are right as well. Gravesites are also popular breeding grounds for container mosquitoes, with plenty of unattended flowers in vases; the mosquitoes can make their way down inside the vases and lay eggs.
Step 3: Treat Water Sources
When you find a particularly nasty infestation, go straight to the source: the water source that is.
There are a few different products that can be used to treat water sources, especially in areas where people may not be able to sacrifice their containers, like rainwater barrels.
The first is Bti, a bacterium that kills black fly and mosquito larvae when ingested, and is used in horse troughs and bird baths. It comes in granular or briquette formulations that last for seven up to 30 days.
But there is a catch — Bti is effective up until the mosquito larva stops feeding, towards the end of the 4th instar. Once the larva reaches the 4th instar, it stops feeding, which means it would not ingest the treated water.
Another option is methoprene, which is an insect growth regulator (IGR). Although IGRs don’t kill mosquitoes immediately, they prevent them from becoming functioning adults. Methoprene, like BTI, is also available in granules or briquettes that last anywhere from 30 to 150 days for a larger briquette.
If you’re in the process of inspecting and treating potential water sources, and you want to check if one does, in fact, house container mosquito larvae before you treat it, Connelly has a quick and easy method.
“One of the ways we go about finding larvae in some of these habitats is to take a turkey baster, a very inexpensive tool, and just suck the water up from an area like this, squirt it into something with a white bottom like a white pan,” she said. “If you see your little wigglers in there then it’s a source that hopefully you can do something about.”
Step 4: Adulticiding
Targeting adult container mosquitoes is a particularly challenging process because of their cryptic habitats, said Connelly.
“They’re resting under vegetation in people’s backyards and it’s really hard to get a space spray in an area where you’re going to impact these mosquitoes,” she said.
Although the results aren’t guaranteed, some pest control professionals and homeowners use a barrier spray on their vegetation.
“The idea is when the mosquito lands on the treated vegetation it will come into contact with this product and it will kill the mosquito or they’ll transfer it to a new larva cycle and they won’t have any offspring,” Connelly said.
Another challenge is that mosquitoes can become resistant to the pyrethroids in these adulticides, like many have in central Florida and the Florida Keys, according to Connelly. “This is something I would use as a last resort; you really want to try and target those earlier stages to prevent them from ever becoming adults,” she said.
Step 5: Surveillance
According to Connelly, surveillance is the step that ties it all together.
“This is really the underlying technique for everything we’ve been talking about,” she said. “If you’re going to apply some treatment you want to make sure the mosquitoes are there so you can look in the containers and look for larvae.”
Connelly suggests putting out a cup of water with a popsicle stick inside at the base of a tree. Check back every couple of days to see if there are eggs stuck along the water line of the stick or cup to get an idea of how many mosquitoes are even out there.
“You can also do this after a treatment to see if the treatment is actually working. Are you reducing the number of eggs in that area?” she said. “Just don’t forget about it because then it can become a source.”
The author is a Cleveland-based freelancer and can be contacted at firstname.lastname@example.org