Now that we’re getting plenty of rain and the temperatures are nice and toasty, our nemesis to enjoying the outdoors is back in full force. Yes, I’m talking mosquitoes, the reason for inventing window screens! If you’re gardening outside these days, you’ve probably been annoyed by one of the many mosquito species that occur in our area. Many of these mosquitoes are native species that play an important role in the food chain, feeding many aquatic and terrestrial wildlife, but some of them, like the daytime biting Asian tiger mosquito, are invasive species that were accidentally introduced. While mosquitoes are an important food source to more charismatic critters, they are annoying and can spread disease, and so we can benefit by reducing their presence.
The Asian tiger mosquito, another annoying invasive species. Photo credit: Susan Ellis, Bugwood.org.
In addition to the age-old advice of draining any standing water, there are other control methods that can be very effective at reducing the mosquito population. One of the most effective and least-toxic options is the use of Bti products. These products come in granular or “donut” forms with the smaller granules being best for various uses around the home and the dunks/donuts for larger areas of standing water like ponds. These Bti products are considered a type of biological control since it is a species of bacteria, Bacillus thuringiensis israelensis to be precise, that causes mosquito, blackfly, and fungus gnat larvae to perish as they wiggle around and grow into their pupal stage. Because it only affects a narrow range of species, it is considered a selective pesticide that does not cause harm to non-target species, such as bees, birds, butterflies, frogs, lizards, and other desirable garden visitors. Bti can be sprinkled into rain barrels, bird baths, bromeliads, gutters, and other places where water may stand more than 5-7 days, the amount of time needed for mosquito eggs to develop into adults.
Bti granules prevent mosquito larvae from becoming biting adults. Photo by: Mark Tancig, UF/IFAS.
If considering other methods of mosquito control, such as the use of foggers, keep in mind that many of the pesticides used to control adult mosquitoes are not selective products and can kill the pollinators you may be trying to invite to your garden. Additionally, planting citronella plants, eating copious amounts of garlic, wearing repellent bracelets, or using ultra-sonic devices or cell phone apps has not been shown to repel mosquitoes so stick to what is known to work.
For a more enjoyable mosquito season, keep the window screens tight, wear long pants and sleeves and use appropriate repellents when outdoors, and do your best to minimize standing areas of water. If you have questions about mosquitoes and their control, visit the UF/IFAS Florida Medical Entomology Lab website (https://fmel.ifas.ufl.edu/) and browse the many resources available.
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A natural disaster such as Hurricane Michael can cause excess standing water which leads nuisance mosquito populations to greatly increase. Floodwater mosquitoes lay their eggs in the moist soil. Amazingly, the eggs survive even when the soil dries out. When the eggs in soil once again have consistent moisture, they hatch! One female mosquito may lay up to 200 eggs per batch . Standing water should be reduced as mush as possible to prevent mosquitoes from developing.
You should protect yourself by using an insect repellant (following all label instructions) with any of these active ingredients or using one of the other strategies:
DEET
Picaridin
Oil of lemon eucalyptus
Para-menthane diol
IR3535
An alternative is to wear long-sleeved shirts and pants – although that’s tough in our hot weather
Wear clothing that is pre-treated with permethrin or apply a permethrin product to your clothes, but not your skin!
Avoid getting bitten while you sleep by choosing a place with air conditioning or screens on windows and doors or sleep under a mosquito bed net.
Now let’s talk about mosquito control in your own landscape.
Let’s first explore what kind of environment in your landscape and around your home is friendly to the proliferation of mosquitoes. Adult mosquitoes lay their eggs on or very near water that is still or stagnant. That is because the larvae live in the water but have to come to the surface regularly to breeze. The small delicate larvae need the water surface to be still in order to surface and breathe. Water that is continually moving or flowing inhibits mosquito populations.
Look around your home and landscape for these possible sites of still water that can be excellent mosquito breeding grounds:
bird baths
potted plant saucers
pet dishes
old tires
ponds
roof gutters
tarps over boats or recreational vehicles
rain barrels (screen mesh over the opening will prevent females from laying their eggs)
bromeliads (they hold water in their central cup or leaf axils)
any other structure that will hold even a small amount of water (I even had them on a heating mat in a greenhouse that had very shallow puddles of water!)
You may want to rid yourself of some of these sources of standing water or empty them every three to four days. What if you have bromeliads, a pond or some other standing water and you want to keep them and yet control mosquitoes? There is an environmentally responsible solution. Some bacteria, Bacillus thuringiensis ssp. israelensis or Bacillus sphaericus, only infects mosquitoes and other close relatives like gnats and blackflies and is harmless to all other organisms. Look for products on the market that contain this bacteria.
In north Florida, the arrival of warm weather and plenty of rain means it’s time to battle the mosquitoes again. Those pesky little blood-suckers are out and about, often keeping us from enjoying our outdoor pursuits. With some preventative steps, you can reduce the potential for mosquitoes to occur in your yard.
Mosquito larvae. Credit: Florida Medical Entomology Laboratory.
As we should all be aware of by now, mosquitoes require water to complete their lifecycle. Eggs are laid near the water and will dry out if they do not remain near a water source. The larvae, or “wrigglers”, that hatch from the eggs, are aquatic and will not survive out of water. The pupae, often called “tumblers”, are also aquatic and must be in water to survive. From the pupae hatch the adults, the growth stage we want to avoid.
Mosquito pupae. Credit: Florida Medical Entomology Laboratory.
The best method to reduce mosquitoes in your yard is to remove or empty water-holding containers. This prevents the conditions needed for the egg through pupae stages to survive. These water-holding containers can include birdbaths, old buckets, gutters, tarps, rain barrels, and a variety of other items. Even a small bottlecap is enough to breed mosquitoes. Regularly emptying these water-holding containers every 3 to 5 days will stop that most annoying final life stage – the biting adults.
Another way to prevent the aquatic stages of mosquitoes from thriving is to use a larvaecide, specifically Bti. Bti is a bacterium that is sold as either small dunks or doughnuts and can also be found as small granules. Placing a dunk or a few granules in a birdbath will prevent larvae from developing and won’t harm the birds or other organisms that may visit, including frogs, bees, butterflies, and mammals. Bti is a selective pesticide, only effective for control of mosquito, midge, and fungus gnat larvae.
Various mosquito breeding habitats. Credit: Mark Tancig, UF/IFAS
Even if you’ve cleaned up or drained all water-holding containers on your property, there will likely still be some adult mosquitoes looking for a bloodmeal. Wearing long pants and sleeves, using mosquito repellents, and keeping window screens in good order are effective methods to prevent being bitten.
Local mosquito control agencies will often provide services to fog for adults. However, this will want to be your last resort, as the pesticides used to control adults are not as selective as the Bti used for the larvae. This results in non-target damage, meaning that insects besides mosquitoes, including beneficial insects, may also be harmed. Therefore, controlling mosquitoes during their aquatic lifestages helps reduce the need for pesticides that can harm beneficial insect populations.
The UF/IFAS Florida Medical Entomology Laboratory Research and Education Center has a great website – https://fmel.ifas.ufl.edu/ – of mosquito-related information, including the various species of mosquitoes in Florida and which repellents work the best. For additional information on controlling mosquitoes and other pests, please contact your local Extension Office.
