Mosquito Bits vs Dunks (Canada 2026): Kills Larvae Faster

How Mosquito Bits Work

Mosquito Bits are corn-cob granules coated with BTI (Bacillus thuringiensis subspecies israelensis) — a soil bacterium discovered in 1976 that specifically targets the digestive systems of mosquito and black fly larvae. The corn-cob granules float briefly when sprinkled onto water, then sink as they absorb moisture. As the bits dissolve, they release BTI proteins into the water column where larvae filter-feed. Not sure the wrigglers you found are mosquito larvae? Our mosquito larvae identification guide shows exactly what to look for before you treat.

BTI is one of the most species-specific insecticides ever developed. It acts on mosquito larvae, black fly larvae, and a few related midge species, which have to eat it for it to work. BTI larvicides are registered for sale in Canada under the Pest Control Products Act. On drinking water its position is precise and worth stating exactly, because it is widely misreported in both directions: no product containing Bti may be applied to treated, finished drinking water for human consumption, but the PMRA has no human health and safety concerns about applying registered Bt products to bodies of water that will later be used for human consumption. The timings quoted throughout this guide — full larvae kill within 24 hours, 7–14 days of control from Bits, about 30 days from a Dunk — are Summit’s own product-label figures, not our field measurements.

How Much to Actually Use: The Label Rates

The number on the front of the bag is a coverage area, not a dose, which is why most people badly over-apply. Summit’s U.S. label (US EPA Reg. No. 6218-86) gives the real rates, and they are small. They are U.S. rates for a product with no Canadian registration; in Canada, use the doses on the registered labels in the table above:

• 1 teaspoon per 25 sq ft of water surface — the correct dose for a bird bath, a bucket, or a plant saucer
• 1 tablespoon per 75 sq ft — a small ornamental pool, or a wheelbarrow that filled up in the rain
• 4 oz per 1,000 sq ft in relatively clean water
• 8 oz per 1,000 sq ft where the water is deep, polluted, heavy with organic matter, or holding large late-stage larvae — decaying leaf litter binds up BTI, so a stagnant ditch needs roughly double the dose of a clean rain barrel
• Re-apply every 7–14 days for as long as larvae keep appearing

The granules themselves are 2.86% Bacillus thuringiensis subspecies israelensis (strain SUM-6218) and 97.14% inert corn-cob carrier, and Summit’s label states a potency of 200 Aedes aegypti Units per mg, or 91 million such units per pound. Resist reading that as a strength score. The same label says plainly that the percent active ingredient does not indicate product performance and that potency measurements are not federally standardized — which is precisely why a bare “contains BTI” claim, and even the percentage beside it, tells you so little when comparing one brand against another.

Two things the rates imply but never spell out. BTI has to be eaten to work, so it only reaches larvae that are actively filter-feeding — pupae have stopped eating and will still hatch, which is why a treated barrel can produce one last small batch of adults a day or two after you treat it. And BTI does not persist: it degrades in sunlight and settles out of the water column. The 7–14 day interval is a genuine re-treatment schedule, not a marketing figure, and it is the single most common reason people conclude the product “stopped working.”

Mosquito Bits for Fungus Gnats in Houseplants

A large share of Canadians searching for Mosquito Bits are not treating a rain barrel at all — they are trying to kill fungus gnats in houseplant soil. That use is on Summit’s U.S. label: fungus gnat larvae, usually Bradysia species, are a labelled target pest alongside mosquito and black fly larvae, and the same BTI that kills a mosquito wriggler kills a gnat larva in potting mix.

Summit’s label gives a soil-drench method, known informally as “gnat tea”:

1. Mix 4 tablespoons of Bits per 1 gallon of water (roughly 60 mL per 4 L).
2. Let it steep 30 minutes, then skim off the floating granules — or steep the bits inside a nylon stocking so there is nothing to skim afterwards.
3. Stir, then water your plants with the treated water, wetting the soil surface where the larvae actually live.
4. Repeat weekly for three weeks. This is the step people skip and the one that decides the outcome: the drench kills larvae but not eggs and not flying adults, so three weekly rounds are what carry you through the full life cycle.

You can also just sprinkle the dry granules over the soil surface and water them in. It works, and it is easier, but the dose is uncontrolled and wet corn-cob can grow surface mould in a pot that never dries. The drench is the cleaner method indoors; dry sprinkling is fine for outdoor containers.

Under the U.S. label, Bits beat Dunks indoors. A dunk is engineered to dissolve slowly across about 30 days, so steeping one for a gnat drench takes roughly 24 hours and still gives you a weaker, less predictable brew — and a quarter-tablet sitting in a plant pot looks exactly as odd as it sounds. Bits release their BTI in about half an hour, which is the whole reason the houseplant world standardised on them. In Canada, Bits have no registration and the Mosquito Dunks label covers mosquito larvae in water only (see the note above).

BTI is only the larval half of a gnat problem, though. The adults you see flying need sticky traps, and the reason larvae are there at all is soil that stays wet too long — our fungus gnat guide for houseplants covers the watering fix and the trap-plus-drench combination that ends an infestation instead of just suppressing it each week.

Buy the traps at the same time as the Bits, because the drench on its own will never make a room feel gnat-free. Yellow sticky cards intercept the adults already flying, which is both the half of the problem you can see and the half still laying eggs back into the pot. They also tell you when you are finished: three weekly drenches plus a card that has stopped filling up is what the end of an infestation actually looks like. Check yellow sticky traps on Amazon.ca →

When to Use Bits Instead of Dunks

In Canada, read “Bits” in this list as a registered BTI granule such as AquaBac 200G (Reg. No. 27374) or My-Crobe 200G (Reg. No. 34631), because Summit’s Bits carry a U.S. registration and no Canadian one. Then skip the gutter, the kiddie pool and the catch basin, because the Canadian labels say “DO NOT apply this product to any water that is designed to flow beyond your property limits (for example, ditches, drains, rain gutters or catch basin sumps that flow into weeping tile beds or municipal storm drain systems)”, and the granule labels add “Do not apply to treated, finished drinking water reservoirs, drinking receptacles and wading pools.”

• You found larvae unexpectedly — wriggling in a saucer or an old bucket — tip the water out if you can; if not, the registered granules’ labels say “Allow 24 hours for maximum effect on larvae”
• Small water sources you cannot change weekly, such as plant saucers, where a floating dunk tablet would be visually awkward; a bird bath needs fresh water twice a week instead (Health Canada), and the granule labels rule out wading pools
• Pet water bowls left outside — tip out and refill daily; only add a larvicide to animal water if the label on your package lists it
• Drainage trays under outdoor planters
• Tarp-covered boats with rainwater pooled on top
• Septic tank ventilation pipes that can hold water
• Storm drain catch basins: not these; the Canadian labels exclude catch basin sumps that flow into weeping tile beds or municipal storm drain systems

When Dunks Are Better

On the Canadian Mosquito Dunks label (Reg. No. 28888) the dose goes by water surface, not gallons: a quarter dunk for “0.1 to 3.0 sq. metres”, which covers a rain barrel, and no ditch that drains off your property.

• Rain barrels — drop one dunk per 50 gallons, replace monthly
• Decorative ponds with fish — slow-release lasts the season, and fish are not a BTI target
• Neglected swimming pools with accumulated rainwater
• Drainage ditches that hold water for weeks
• Tree holes and stump cavities
• Any standing water you can’t check on weekly

The Smart Approach: Use Both

Plenty of homeowners end up using both formats. The dunk goes in the rain barrel for set-and-forget protection — drop it in May, forget about it until June. The granules sit in the garden shed for emergency use whenever you discover larvae somewhere unexpected; in Canada that means a registered BTI granule such as AquaBac 200G or My-Crobe 200G, not Bits.

For a typical GTA backyard with one rain barrel and a few potential standing-water spots, BTI is the cheap half of the job: one 6-pack of dunks covers the rain barrel for the full May–September season, and a container of registered BTI granules handles every other standing-water situation that comes up. For the other half, what professional mosquito control costs starts at $99 for a single treatment and scales with lot size. On a typical suburban lot — the kind a Markham mosquito control quote covers — the BTI still earns its keep, it just cannot reach the adults.

Bits + Barrier Spray: The Complete Mosquito Strategy

BTI bits and dunks solve the LARVAL side of mosquito control — but they only work on water you actually treat. Adult mosquitoes flying in from neighbours’ yards, ravines, and creeks are unaffected. On the deep, tree-lined lots north of the city this is most of the problem — a sprinkle of BTI granules in the plant saucers does nothing about what is already flying, which is the gap mosquito control in Vaughan is built to close. For a fuller plan in your GTA backyard:

1. Registered BTI (Mosquito Dunks, Reg. No. 28888, or a registered granule) in the standing water on your property that its label covers
2. Habitat modification — drain anything you can drain, mow short, clear leaf litter
3. Professional barrier spray — BuzzSkito’s seasonal program targets adult mosquitoes flying onto your property, with a registered residual formula applied according to label directions and renewed on a schedule

One note on the standing-water audit in step two, because it usually stops at the back door: the sump pit, the floor drain whose trap has dried out, and the laundry tub with a weeping trap are standing water too. They matter less for mosquitoes than a rain barrel does, and they matter a great deal for the damp-basement insects that share the same water — which is why our silverfish trap buying guide and centipede product guide both start with the humidity rather than with a spray. Lidding the pit and pouring water down seldom-used drains takes ten minutes and closes several problems at once.

That three-part stack covers mosquitoes, but BTI is only one product on a much longer Canadian shelf — our pest product guides group everything we have researched, from larvicides and traps through to repellents, by pest and by category.

One device deliberately left off the stack: the UV bug trap. It is the first thing most homeowners buy and the layer that does the least — independent trap research puts mosquitoes under 5% of what a UV-plus-fan trap catches. If you are weighing one against a season of BTI, we break down whether DynaTraps actually work on mosquitoes, model by model.

Are Mosquito Bits Legal in Canada? What the PMRA Actually Says

Not as Mosquito Bits. BTI itself is legal here, in registered products such as Mosquito Dunks (Reg. No. 28888), but registration is product by product, and Health Canada’s pesticide registry, searched on October 23, 2026, has no product named Mosquito Bits, current or cancelled. Summit’s bag carries U.S. EPA Reg. No. 6218-86. The Pest Control Products Act is blunt about unregistered products: “No person shall manufacture, possess, handle, store, transport, import, distribute or use a pest control product that is not registered under this Act” (section 6(1), which lists narrow exceptions). The question keeps resurfacing because the regulatory picture has two layers, and searchers keep landing on the wrong one.

Health Canada’s Pest Management Regulatory Agency (PMRA) registers every pesticide sold in Canada, and each registered product carries a PCP (Pest Control Products Act) number on its label. In its Bti fact sheet, the PMRA states that nearly all products containing Bti are Restricted class products “used to control black fly and mosquito larvae in aquatic situations where the flow of water is not confined to a small area,” and adds that commercial class Bti products can only be used against black fly and mosquito larvae in private ponds and farm dugouts where no outflow beyond the property limits exists. Both of those classes describe the large-volume job a municipality or licensed applicator does on open water — a creek, a marsh, a farm dugout — rather than anything in a backyard.

One honest caveat about that reasoning, because the same fact sheet says two different things. In a later section it gives a different ground for the same classification: that the PMRA has classified nearly all Bti products as Restricted “since they must be applied only in the water where the larvae exist.” That sentence would apply to a rain barrel as readily as to a creek, so the confined-water wording is not by itself a complete explanation, and we are not going to pretend it is. What actually decides the question is narrower and checkable: a pesticide’s class is set by its own registration, product by product, and domestic-class products are the ones sold to consumers without a licence. That is why the number on your package, not the general wording of an archived fact sheet, is the thing to look up.

Two caveats worth stating plainly. That PMRA fact sheet is marked ARCHIVED, last updated 4 May 2017, so treat it as background rather than the current rulebook. And the authoritative check for any specific product is the live PMRA Pesticide Label Search database: take the PCP number printed on the package in your hand and look it up. A US EPA registration number on an imported bag is not a Canadian registration — that distinction is the actual substance behind most “is this legal here” confusion.

On safety, the same PMRA fact sheet is worth quoting precisely, because it is routinely paraphrased too loosely in both directions. The PMRA states that no product containing Bti may be applied to treated, finished drinking water for human consumption. Separately, it states that the agency has no human health and safety concerns about the application of registered Bt products to bodies of water that will be used for human consumption. In plain terms: BTI is not something you add to a municipal system or a kitchen tap, and it is not regarded as a health hazard where it is applied to raw water bodies under its registered uses.

The “Bucket of Doom” and the 2026 Canadian Dunk Shortage

If you went looking for dunks in June 2026 and found empty pegs, you were not imagining it. CBC News reported that mosquito dunks were selling out as bug season collided with the “bucket of doom” trend; a manager at a Home Hardware on Bank Street in Ottawa told CBC that his store was sold out by mid-June and so was the company’s warehouse. Cottage Life covered the same DIY trend through the summer. That shortage, not any regulatory action, is the origin of most of the “you can’t get these in Canada” chatter.

The technique is simple, and it is the one situation where the Bits-versus-Dunks question genuinely changes shape. Fill a five-gallon bucket with water, add a handful of grass clippings, straw or leaves, and let it sit until it goes properly foul. Female mosquitoes strongly prefer that organic stink to clean water, so the bucket becomes the most attractive place in your yard to lay eggs. Add BTI, and every egg laid there dies as a larva. It is an attract-and-kill trap built out of the mosquito’s own preferences rather than against them.

Under Summit’s U.S. label this job points toward Bits: bucket water is deliberately deep, dark and loaded with organic matter, which is precisely the condition Summit flags as needing the higher 8 oz per 1,000 sq ft rate, and Bits let you top the dose back up on the 7–14 day schedule as the brew degrades. In Canada, Bits have no registration, so the BTI option is a registered product such as Mosquito Dunks (Reg. No. 28888), used only as its label directs. Whichever you use, the bucket has to be re-dosed all season — an untreated bucket of doom is just an unusually effective mosquito nursery, and that is the failure mode to take seriously before building one.

The counter-argument deserves airing, because it surfaces every time the trend does. Aquatic and wildlife-pond hobbyists point out that BTI is not perfectly selective even within its own corner of the insect world: it also affects some non-target chironomid midges, the harmless lake flies whose larvae feed dragonfly nymphs, fish and birds. That is a fair point, and it is consistent with what BTI is — a larvicide for mosquitoes, black flies and a few closely related midges, not for insects generally. It does not change the evidence that BTI acts on those larvae rather than on people, pets, fish, amphibians or pollinators. What it does mean is that an established wildlife pond running as a real ecosystem is a poor candidate for routine BTI, while a rain barrel, a bird bath, a tarp puddle or a purpose-built bucket support no midge food web worth protecting and cost you nothing ecologically. Treat the containers; leave a healthy pond alone unless it is genuinely producing mosquitoes. Where a pond is the problem, moving the water with an aerator stops egg-laying without adding anything to it at all, since mosquitoes will not lay on a disturbed surface.

That aerator point is worth acting on if a pond is the water in question, because it is the one fix that needs nothing added to the pond at all. A female will not lay on a surface that is moving, so a small fountain pump or a solar aerator takes the pond out of the mosquito’s list of options while leaving the midge and dragonfly food web exactly where it is. Check pond aerators and fountain pumps on Amazon.ca →

Other BTI Formats Sold in Canada — and One Canadian Product That Is Not BTI

Bits and Dunks are the two consumer formats, but BTI is sold in several others, and knowing the names saves you searching for the wrong thing:

• Granular BTI (AquaBac 200G, My-Crobe 200G) — corn-grit granules for broadcasting over larger or vegetated water. Most of their registrations are restricted or commercial class, but each also has a domestic-class version a homeowner may use (Reg. No. 27374 and 34631; see the table above).
• Liquid BTI concentrate (the VectoBac-type products) — measured and diluted for spray application over large sites. Again a commercial-channel product, and one of the aquatic uses covered by the PMRA’s restricted classification above.
• Gnatrol — a BTI formulation made specifically for fungus gnat larvae in greenhouse and nursery growing media. Its Canadian registration (Gnatrol DG Biological Larvicide, Reg. No. 27821) is listed as cancelled in Health Canada’s registry.
• BTI briquets (Summit B.T.I. Briquets, Reg. No. 28995) — the long-life tablet format, essentially the same idea as a Dunk, registered here as a restricted-class product; the older Bactimos products appear only as historical entries.

The important shelf competitor in Canada is not BTI at all. Doktor Doom 90-Day Mosquito Larva Killer briquettes are made by a Canadian company and often sit on the same seasonal shelf as the Summit products, and their active ingredient is novaluron, an insect growth regulator. It is registered in Canada as a domestic class product under PCP registration number 34197 — a useful thing to see, because it is a concrete example of a Canadian-registered consumer larvicide you can look up yourself in the PMRA database. Novaluron does not destroy the larval gut the way BTI does; it stops larvae from moulting successfully, so they never emerge as adults. The label calls for one briquette per 200 litres of water (two where organic matter is high, half a briquette for 100 litres) and rates it for up to 90 days, against roughly 30 days for a BTI dunk. Two lines on that label matter for pond owners. One reads “This pesticide is toxic to aquatic invertebrates.” The other rules out “permanent natural water bodies such as lakes, rivers, streams, creeks, dugouts or ponds”; ornamental ponds holding 100 litres or more are on its list of sites.

The trade-off is real in both directions. If you want a rain barrel handled with one decision in May, a 90-day novaluron briquette is a genuinely longer interval than any BTI product offers. If you have just lifted a lid and found the water squirming, BTI is the faster answer — it kills feeding larvae within about 24 hours, whereas a growth regulator has to wait for those larvae to attempt their next moult. The two are not interchangeable, and a page that only ever mentions BTI is leaving out the product most likely to be sitting next to it on a Canadian shelf.

If a single decision in May is what appeals to you, that briquette is the one to line up against a card of dunks before you commit to a season of either — one drop-in versus a monthly reminder, with the faster knockdown of BTI kept in the shed for whatever you find in the meantime. Check long-interval larvicide briquettes on Amazon.ca →

Black Flies: Why Bits Work on the Label but Not in Your Yard

Black fly larvae are a labelled target for BTI, and BTI genuinely is the standard tool used against them across Canada. For a homeowner, though, the honest answer is usually that Bits will not solve a black fly problem, and the reason inverts everything else on this page.

Black flies do not breed in standing water. They breed in flowing water — in the riffles and runs of streams and rivers, where larvae anchor themselves to rocks and vegetation and filter the current. That is why cottage country, Northern Ontario and much of Quebec have a black fly season that has nothing to do with how tidy anyone’s yard is. Sprinkling Bits into your containerized standing water treats mosquitoes and will not touch a black fly population coming off a creek two properties over.

Treating a flowing watercourse is exactly the restricted-class aquatic use the PMRA reserves for licensed applicators, and it is not a DIY project — dosing moving water requires calculating flow rate, and a consumer pack has no rate table for it. Where black flies are managed in Canada, it is generally through a municipal or regional program that treats watercourses on a schedule. For a property owner, the realistic tools are timing (black fly activity peaks in late spring and collapses in summer heat), physical barriers, and repellents rather than larviciding.

Of those three, the physical barrier is the one that holds up during an actual black fly peak, because black flies crawl rather than hover — into hair, behind ears, in under a collar or a cuff. A head net worn over a brimmed hat, with sleeves and trouser legs closed off, is the standard cottage-country answer, and unlike anything you apply it does not wear off through the evening. Check head nets and bug jackets on Amazon.ca →

Finding BTI on a Canadian Shelf: Names, Numbers and Search Traps

The registered tablet to look for is Summit Mosquito Dunks, Reg. No. 28888 on the label, most commonly a 6-pack card. The registered granules are AquaBac 200G (Reg. No. 27374) and My-Crobe 200G (Reg. No. 34631); phone ahead for those. Summit Mosquito Bits, the orange and green bag in 8 oz and 30 oz sizes (the 30 oz bag is Summit’s model number 117-6), carries a U.S. EPA number and no Canadian one. In-store, larvicides are almost never with the aerosol insecticides — look in lawn and garden, or in the seasonal pest aisle that appears in spring and disappears in September, which is a large part of why the product seems to vanish from stores in the autumn.

One search trap is worth knowing because it costs people real time. On Google.ca, the Home Depot result that ranks highest for “mosquito bits” is frequently the US homedepot.com product page rather than the Canadian one. It shows US sizes, US pricing and US stock, none of which apply to a store you can drive to. The same happens with Amazon search pages that mix US and Canadian listings. Search homedepot.ca or canadiantire.ca directly and check availability by postal code rather than clicking a general Google result and assuming it reflects Canadian stock.

Timing matters more than retailer choice. BTI is a seasonal line, the 2026 shortage showed how quickly a national warehouse can empty, and shelves thin out from mid-June onward. April and May are when the full range is present at every chain; by late July you take what is left. If your yard has more than one water source, the standing-water audit in our rain barrel mosquito-proofing guide is worth doing before you buy, because it tells you whether you need one container or three.

Related Reading

• Mosquito Dunks Canada — Complete Guide
• Hidden Mosquito Breeding Spots in Your Backyard
• Natural Mosquito Repellent — What Actually Works
• How to Get Rid of Mosquitoes in Your Yard (Ontario)
• The Ultimate Backyard Mosquito Control Guide
• Do DynaTraps Actually Work on Mosquitoes?
• Best Wasp Traps in Canada — Bag, Sticky & Reusable Compared
• How to Get Rid of Fungus Gnats in Houseplants
• How to Mosquito-Proof a Rain Barrel in Canada
• Pond Aerators vs Mosquito Larvae
• Mosquito Larvae Identification — What Is Actually in Your Water
• BuzzSkito Professional Mosquito Control Service

Frequently Asked Questions