Sterile mosquitoes vs larvicides and dunks

How larvicides and source reduction work

Mosquitoes start life in water. Stop them there, and they never become biting adults.

Source reduction comes first

Mosquitoes breed in standing water, especially water that stands for at least 7 days. Texas A&M AgriLife Extension's first step is to drain, dump or fill it: buckets, flowerpot dishes, tarps, wheelbarrows, birdbaths, old tires and clogged gutters. Fill low spots with sand or gravel, and seal tree holes.¹ It costs nothing and helps every other method work better.

Larvicides for water you can't dump

• Bti (Bacillus thuringiensis israelensis) is a natural soil bacterium sold as dunks, briquettes and granules. The EPA says its toxins affect only the larvae of mosquitoes, black flies and fungus gnats, that it has no toxicity to people, and that there is no documented resistance to it.³ AgriLife says a small amount is effective for up to 30 days¹, and NC State Extension says dunks last around 3 to 4 weeks.²
• Methoprene is an insect growth regulator. It stops larvae from completing development, so they never reach adulthood.⁴ Depending on the formulation, AgriLife says it may last more than 30 days.¹
• Other larvicides include spinosad, oils and films. The CDC notes that one bacterial larvicide, Lysinibacillus sphaericus, does not work on the yellow fever mosquito.⁴

Cities use the same tools at scale. Dallas Code Compliance applies larvicide to known breeding sites and treats storm drains where trap collections show a need.⁵

The catch

AgriLife puts it plainly: you must know where the mosquitoes are breeding, and you must reapply through the season.¹ That's hard with Asian tiger and yellow fever mosquitoes, which lay eggs in small containers and tree holes, often in neighbors' yards within a few hundred yards of yours.¹ And larvicides don't touch adults already flying: Bti "does not control biting female mosquitoes," per the CDC.⁴

How sterile males work

We release sterile male Asian tiger and yellow fever mosquitoes, the species that bite in yards by day and at dusk. Males don't bite. A dunk works in the water you find. Our males find wild females on their own, including near the gutter, tree hole or saucer nobody spotted, and their eggs don't hatch. It's precisely targeted: it affects only the two mosquito species we release, and nothing is applied to water, plants or soil.

Side by side

Larvicides, source reduction and sterile males each work on a different part of the life cycle.

When larvicides are the right choice

Almost always, alongside something else. Larvicides aren't a rival to sterile males so much as a teammate.

Water you can't empty. Ornamental ponds, rain barrels, retention ponds, water hazards and drains are where dunks and granules earn their keep.

Night biters. Our releases reduce Aedes only. Night biters breed in storm drains and ponds,⁷ where larvicides are one of the main tools.

Low-risk by design. Bti is about as targeted as a mosquito product gets: the EPA says it affects only a few kinds of fly larvae and has no toxicity to people.³

Using them together

This is the combination public programs use. In a California district, releases cut female mosquitoes by 44% with sterile males alone, and 65% combined with In2Care larvicide stations.⁶ That's evidence for the method, not SMF's own result.

The two don't get in each other's way. Bti and methoprene act on larvae in the water, while our sterile males are adults looking for mates. So a sensible plan for many properties is:

• Every week after rain: tip out containers and clear gutters.
• Water you can't dump: a Bti dunk, replaced every few weeks.
• All season: sterile male releases for the daytime and dusk biters.

Comparing other tools? See mosquito traps, natural mosquito control and bats and mosquitofish, or Compare all options.