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Guide to Mosquito Dunks [Review + Alternatives]

Mosquitoes are everybody’s least favorite insect. From their painful, itchy bites to their ability to spread diseases, most of us would be happy never to see a mosquito again.

Because mosquitoes breed around still water, they can find plenty of places to breed around your home. Bird baths, gutters, rain barrels, piles of trash (especially old tires), ditches, and flowerpots are just some of the places that mosquitoes love to breed.

Mosquito larvae found in an outdoor grill’s grease trap

Before you throw out that beautiful antique bird bath, there is a solution. When it’s impossible or undesirable to get rid of standing water around your home, a Mosquito Dunk may be just the solution you need. Read on to learn more about how Mosquito Dunks work and whether they might be right for you.

How Mosquitoes Breed

One of the tough things about mosquitoes is that they breed rapidly. In the wild, mosquitoes breed around ponds and marshes, laying their eggs in shallow water. The young mosquitoes are aquatic and feed on algae and microorganisms in the water. Only when they have matured into adults do they come out of the water and start to fly around.

When it is time to breed again, female mosquitoes will bite a human or animal to drink their blood to get the nutrients necessary to produce eggs. And the cycle continues.

Around your home, this means any sign of still water could mean a big mosquito problem for you in a few weeks.

What Are Mosquito Dunks?

Mosquito Dunk is the brand name of a product made by Summit Chemical Company that is designed to control mosquitoes in the breeding and development phase, unlike other products such as netting and repellants that only work on adults. They also make Mosquito Bits, which have the same active ingredient as the Dunks but it is released instantly instead of a slow release over time.

mosquito dunks

The premise is simple – throw a Dunk into standing water, and it floats across the top slowly releasing an agent that kills the mosquito larvae. The brilliance of mosquito dunks is in what they release. You would think it would be a pesticide, but it’s actually a specific kind of bacteria –  Bacillus thuringiensis serotype israelensis.

And if that’s as exhausting for you to read as it was for me to write it, we can both just call it by its nickname – Bti.

How Bti Kills Mosquitoes

Bti is the perfect biological control agent, which means it’s an organism that has been found to selectively kill a pest organism without harming the rest of the environment. Biological control is a huge part of modern pest management, but you don’t hear about it as much because it’s a lot slower than pesticides in most cases, so it doesn’t work for household pests. Bti is a rare exception of a biological control agent where you can see results right away!

It works by releasing toxins into the guts of larval mosquitoes. It also works on other flies like black flies and fungus gnats. And mosquitoes that die as larvae can’t grow up to become bloodsucking pests.

How to use Mosquito Dunks

Mosquito Dunks are pretty straightforward, but it’s important to make sure you are using the right product and the right amount. Other than that, there’s not much of a learning curve to Mosquito Dunks – you pretty much just throw them in the water you’d like to treat and walk off.

Mosquito Dunks or Mosquito Bits?

There are two main products available on the market that contain Bti – Mosquito Dunks and Mosquito Bits. The only difference is the time it takes to release the Bti. Mosquito bits are like a big instantaneous blast of Bti, whereas the dunks release it more slowly. Bits are great if you know larvae are there already and you need to kill them before they can emerge. Dunks are better for preventative treatment and maintenance.

How Many Dunks to Use?

Always make sure to check the labels on whatever product you purchase. How much to use depends on how much water you have to treat. Surface area is more important than volume for deciding how much to use since mosquitoes breed and live close to the surface.

A general rule of thumb is one dunk per 100 square feet of surface area of water. For small areas, dunks can be split into quarters, using one quarter for every 25 square feet. The treatment lasts about 30 days, but there’s no harm in putting in the next Dunk a few days early just to be safe.

For Mosquito Bits, you should use about one teaspoon for every 25 square feet or a tablespoon for every 75 square feet of surface water, sprinkling it evenly over the surface of the water. Mosquito Bits are meant for quick applications, so they don’t last long. It shouldn’t be necessary to treat with Mosquito Bits more than once every two weeks, because it takes a while for mosquitoes to lay more eggs and for those eggs to hatch.

Both products can be stored in a cool, dry place (avoid hot sheds!) and remain potent for up to two years. After that, they may still work, but might not be as strong. When in doubt, buy a fresh batch and try to use it over the course of the season.

Alternatives to Mosquito Dunks

As far as small-scale Bti products, Mosquito Dunks and Mosquito Bits are pretty much the only skin in the game, so you don’t need to do a lot of shopping around. That said, if you’re willing to spend a bit more at the offset to stock up, there are industrial-sized formulations of Bti available on the market. These are usually used by pest-control and environmental professionals to treat entire ponds for the season.

These industrial-grade products allegedly can be stored in a cool dry place, but there is not a lot of information available on exactly how long you can store them and maintain their effectiveness (because they’re usually used quickly). So in most cases the Bits and the Dunks will do the job just fine.

Mosquito Dunk FAQ’s

Do Mosquito Dunks kill adult mosquitoes?

No. Bti is unfortunately only toxic to larvae.

What time of year should I put in Mosquito Dunks?

Mosquito season varies a lot across the country, so check your mosquito season in your state, and aim for two weeks to a month before it begins to start putting in your Dunks. If you see any mosquitoes before then, regardless of whether they are near your home, put in the Dunks as soon as possible. Mosquitoes live for at most a month but are often killed by predators before then, so it’s not that hard to catch up to them.

Are Mosquito Dunks safe for pets and other animals like tadpoles, fish, birds, etc.?

Absolutely! The brilliance of Bti and why it is so much better than pesticides is that there is no danger to other species (though it is toxic to other types of fly). So don’t worry a bit about your pets, children, or local wildlife. Only the mosquitoes are in danger.

Can I put Mosquito Dunks into a pool? What about a kiddie pool?

Yes. Mosquito Dunks are safe to use in pools, even in kiddie pools. Bti doesn’t harm humans or cause any skin infections. However, you should probably take the dunk out of the pool before you let your children in to keep them from playing with it or putting it in their mouths. I can’t say for sure what would happen if somebody tried to eat a Mosquito Dunk, but it can’t be better than not eating it.

The only risk currently associated with Bti for humans is potential eye and skin irritation. For this reason, it’s best not to put large amounts of Mosquito Bits in any place you plan to swim. You may want to avoid using Mosquito Dunks or Bits if you or somebody in your family has especially sensitive skin.

Can I use Mosquito Dunks in potted plants?

Bti is great for potted plants because it controls fungus gnats. However, mosquito dunks can’t be used in potted plants straight out of the package because there isn’t enough water in a potted plant to release all the Bti. So the best way to use a Mosquito Dunk is to put a quarter of a Dunk into a gallon of water and let it rest overnight. Then you can use the water to water your plants. Mosquito Bits will also do the trick, but make sure to use this water right away, since Mosquito Bits are not meant to last long. Do this about once a week to keep the fungus gnats far away!

Can Mosquito Dunks be used for a whole pond?

Theoretically, yes. However, you would need a lot of them to make much of a difference. In general, ponds are treated with industrial-scale liquid formulations of Bti. And pond treatment is best left to professionals, since even if mosquitoes are annoying to us, they are an important part of food webs and treating with Bti could disrupt the ecosystem of the pond, doing more harm than good.

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Written by Miles Martin

Miles is a professional science writer with a Bachelor of Arts in Biology from the University of Rhode Island and a Masters of Science in Science Communication and Public Engagement from the University of Edinburgh.


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    • Roger – it should be fine, however I would contact Summit Chemical Company to be sure. The reason I say it should be fine is because there are tons of Bti products out there specifically intended for garden use pest control. So the bacteria itself will be fine and not affect plants negatively.

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