By Melinda Heigel, NC State Extension Master GardenerSM volunteer of Durham County
(Left to right) Planting for pollinators, like this Eastern tiger swallowtail butterfly (Papilio glaucus), is one of the biggest developments in sustainability today. When out fostering pollinator habitat, gardeners might also want to think about ways to reduce or influence mosquito habitats. Mosquitoes, like this Asian tiger mosquito (Ades albopictus), can make time in the landscape less than enjoyable. (Image credit: Melinda Heigel; NC State Extension)
I recently installed a new garden to support beneficial insects in my small urban landscape. While out babying my new plants, I happily discovered they are already attracting a host of pollinators like butterflies, moths, and all kinds of bees. Sadly, I found that I, the red-blooded gardener, was attracting a ton of mosquitoes when tending my new charges. Turns out that mosquitoes are most active early in the morning and later in the evening. They keep gardeners’ hours in your landscape and are out when you most likely are too. And with all the much-needed rain we are getting this week, female mosquitoes have some lovely new water sources where they can lay their eggs.1 Mosquitoes are not only annoying, but of course they can also transmit diseases to humans like West Nile virus and are the carriers for the parasite that causes heartworm disease in dogs.
There are several steps you can take to make your landscape more fun to garden in and less attractive to mosquitoes. Of course, I can use an insect repellant and wear long sleeves and pants, but I wanted to see what else I could do on a foundational level to impact the number of mosquitoes I am encountering in my outdoor space.
Before I outline some simple, sustainable steps we can all take to control pesky mosquitoes, I want to address one potentially controversial option: residential aerosol fogging. You’ve probably seen signs advertising services to spray your yard with the promise of, “No more bites.” Homeowners can also purchase do-it-yourself products as well. This control practice is called adulticiding as these sprays typically target adult mosquitos that are actively flying at the time of treatment or who will rest on a treated surface while the chemical is still active.
While they can be effective, they have some real drawbacks to consider. They don’t address larvae that will hatch later and continue the insects’ lifecycles.3 Environmental factors like rain can impact the efficacy of these treatments and make them terribly short-lived. It can be expensive. And there is always the possibility of drift when either you or a professional are spraying. This means that wind may carry the product where you don’t want it: into a neighbor’s landscape or into your own bed with flowering plants and pollinators.
Personally, my biggest concern about this method is indeed the health of pollinators (and fish if you have a water source or pond nearby). The most common active ingredient in these products is pyrethroids. These chemicals are toxic not only to adult mosquitoes but also to beneficial insects we want around like beetles, ladybugs, green lacewings, and bees. In my landscape, I am trying to support pollinators, not endanger them. To be sure, employing this chemical control method is an individual choice, but what else can a gardener do that is both effective and wildlife friendly?
Understand the Mosquito Lifecycle
(Left to right) The first three stages in the lifecycle of a mosquito are dependent on water. Mosquito eggs in water. (Imager credit: Centers for Disease Control and Prevention; Lauren Bishop, CDC public domain)
First, know your enemy (Joking, not joking). Mosquitoes have four distinct stages in their lifecycle–egg, larva, pupa, and adult. The most important thing to know about these stages is that the first three occur in water. Only the adults fly for a short time. Females of many species dine on the blood of humans and other animals (Note that males don’t; they feed solely on plant nectar). Once females complete a blood meal, they lay eggs in or near water, soil or near the base of some plants that might collect water. Some eggs can persist in dry conditions for a limited period of time, but water is always a necessary ingredient.
Reduce Mosquito Habitat
After some rain this week, I scouted out places in my outdoor areas where standing water was available to serve as breeding sites: a small amount of rain caught in watering cans, plant saucers, and a pile of reserve mulch material I have covered with a tarp in my driveway. Time to “tip and toss!” (Image credit: Melinda Heigel)
Since water is essential for the completion of the mosquito lifecycle, take a good look around your site. Dr. Michael Waldvogel, NC State Extension Specialist, suggests that “(m)odifying or eliminating breeding sites is the long-term solution to mosquito problems.” He suggests the tip and toss method where you frequently empty containers around your landscape and dwelling that can hold water such as dishes under flower pots designed to catch runoff water, buckets, and empty garden pots (doesn’t every garden have these laying around?). Some types of mosquitoes only need 1 tablespoon of water in which to develop.2
If you have a birdbath or other water source for wildlife in your landscape, flushing those out and refiling with fresh water at least twice a week will help eliminate mosquito eggs, larvae known as wrigglers, and pupa.
If you are into eco-friendly irrigation and have barrels or containers to catch rain water, keep them covered with screening to help with mosquitos and debris. Waldvogel suggests also keeping the screens washed off and clean.
Other culprits you might not suspect include clogged gutters, areas in your landscape that have poor drainage where water might stand, pet bowls, wheel barrows, trash cans, woodpiles, cups and bottles out for recycling, and things like catch basins in your drainage system.
Assemble A Mosquito Dunk Bucket
A simple and effective way to control the non-adult population of mosquitoes in your landscape is with a mosquito dunk bucket, which ends the lifecycle at the larval stage. (Right to left) Here is one in my side yard adjacent to my newly-installed pollinator garden, and this dry donut-shaped object is a biological control (with a bacterium named Bti) for mosquitoes sometimes called a “dunk.” These larvicides also come in other forms, including liquid, pellets, and granules. (Image credit: Melinda Heigel)
While chemical fogs focusing on adult mosquitoes are non-specific, meaning they will harm or eliminate many insects indescriminately, there is a safer more effective method that will only target mosquitos in their larval stage. Enter the mosquito dunk. Looking like a small hard tablet, the mosquito dunk contains a naturally occurring bacterium Bti (Bacillus thuringiensis, subspecies israelensis). When placed in water with mosquito larvae, the larvae ingest the Bti spores and die often within 24 hours. The good news is that Bti target larval mosquito digestive systems and are safe for humans, pets, fish, and beneficial insects.
So how does a dunk bucket work? The dunk bucket approach to mosquito control is sort of like setting a honey pot for female mosquitoes. You are essentially creating a controlled habitat for females to lay eggs that will never mature into adults. Don’t worry — you aren’t likely attracting more mosquitoes to your environment. Remember they are there anyway, and this helps concentrate where breeding is happening.
You don’t need many materials to set up this “Bucket of Doom,” as some folks call it. Just the following:
- Bucket
- Something to cover the bucket like screening or a mesh insert
- Natural material like straw, hay, grass clippings or dried leaves
- Water
- Mosquito Dunk® or other brand containing Bti
(Left) Materials I used for constructing my dunk bucket included a well-fitting bucket lid that had a plastic mesh top. I found this online at a hydroponic growing site, but you don’t have to get fancy. Something as simple as chicken wire or a bucket lid with holes drilled in it will work as long as the females can enter it to lay eggs. I have even seen this step listed as optional, but I wanted to discourage my dog or any other small critters from getting too curious. (Right) I used packaged straw from a hardware store, but again, yard waste like dried leaves or grass clippings will do the trick.
Setting the Dunk Bucket “Trap”
Here are the easy steps to getting your bucket up and running. It will be set to go within a few days.
(Left to right) Adding the straw and water, leaving it in the sun, and waiting a few days before I added the dunk for maximum fustiness. Seriously, though, this doesn’t smell foul. And in the landscape in an out-of-the way site, I never caught whiff of any unpleasant odors. (Image credit: Melinda Heigel)
- Add several big fistfuls of your natural material (hay, straw, dried leaves, etc.) to your empty bucket.
- Fill the bucket about halfway with water.
- Let your bucket sit and get “funky” for a few days. This quasi-fermentation process emits gasses that attract mosquitos. Putting your work-in-progress in a sunny location helps speed up this process.
- After a few days, sit the dunk inside the bucket.
- Place your bucket in the landscape. Mosquitos like a shaded area that is low-traffic, so think about where you can place yours. Another tip is to locate it in areas that are mosquito-prone. I have some larger shrubs close to my house near my pollinator garden where I put my bucket.
Mosquito Dunk Bucket Maintenance and Considerations
You should check your bucket weekly and replace water levels as needed. Remember if you get a lot of rain (wishful thinking during drought), you will also want to make sure your bucket is not overflowing and adjust the water level as needed. The dunk itself will last about a month, so put a reminder on your calendar so you remember to put out a new one. You do not have to dump the contents at any given period, just keep the water level and Bti tablets consistent. At the end of the warm mosquito season, it is safe to just empty the bucket on the lawn.
While a properly-maintained bucket the is indeed controlling mosquitos, remember that a poorly-maintained one actually just becomes a breeding site once dunks are no longer active.
Depending on our outdoor space, you may want to consider adding more than one bucket. Mosquitoes, like most things organic in this world, don’t observe borders or property lines. Dunk buckets are effective, but they don’t eliminate all mosquito pressure. Consider asking your neighbors to join you in this endeavor to try and broaden the scope of this control beyond your immediate landscape.
While tip and toss and dunk buckets aren’t the only methods to control mosquitos and help ensure both gardener and pollinator health, they are easy, inexpensive, and effective especially when used in tandem. I encourage you to give them a try.
Notes
1–According to the US Environmental Protection Agency, the average span of mosquito lifecycle is 2 weeks. Environmental conditions can shorter that to 4 days or lengthen that to up to a month.
2–https://hgic.clemson.edu/hot-topic/importance-of-reducing-mosquito-breeding-sites/
Resources and Additional Information
Why we should care about pollinators
NCSU on mosquito control around homes and communities
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