It doesn’t fix the source.

Spray kills adults flying right now. It does nothing about the standing water already producing the next batch. The mosquitoes come back because the conditions that produce them haven’t changed. Source reduction breaks the cycle instead of just interrupting it.

It only works if your whole block participates.

A treated yard surrounded by untreated yards gets repopulated within days. The coordination that would make spraying effective is the same coordination that makes source reduction and trapping effective — except those actually address the root cause.

The results don’t last — and it’s expensive.

Reapplication every 3–4 weeks through the season, at $75–$150 a treatment. Because new mosquitoes keep hatching from the same untreated breeding sites. That’s several hundred dollars a season to keep resetting the clock.

It kills insects you want around.

Pyrethroids are broad-spectrum and can’t distinguish a mosquito from a bee, firefly, or butterfly. “Natural” sprays based on cedar oil or essential oils are less toxic to mammals but still harmful to pollinators — and equally ineffective against tiger mosquitoes hiding in your shrubs. [National Wildlife Federation]

There’s a better way. You’re already on it.

Source reduction, larvicide treatment, and community-wide trapping. Less immediately satisfying, but the results compound rather than reset — and a BTi dunk costs about $2.