Tag Archives: oviposition

Bti honeypot traps for killing mosquito larvae

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An easy way to kill thousands of mosquitoes each summer is to set out a container of water, add a handful of leaves or hay, then drop in 1/4 of a Mosquito Dunk, a compressed, shelf-stable form of Bacillus thuringiensis israelensis (“Bti”) that kills larvae. Pregnant females will oviposit onto the water surface as well as onto the sides of the container and when the larvae begin to feed they’ll be killed by the toxins produced by the bacteria. Just add a fresh crumble of Mosquito Dunks every three weeks to ensure the system is operating as needed.

Photograph of a green bucket covered with black mesh, resting on a snow-covered step. Next to it is a milk jug filled with water, a container of dried leaves, and a package of Mosquito Dunks.

Tips

  1. Cover the container with chicken wire or netting to prevent birds and chipmunks from drowning.
  2. Add a long stick that can fit through the mesh so that innocent insects that fall into the water have a way to crawl back out. Bonus: some mosquito species increase oviposition rate when wet wood is present.
  3. Add a white object that allows you to see whether there are larvae wriggling around.
  4. Make more than one to maximize the effect.
  5. Set traps out in early spring so that the leaves have time to decompose and become attractive to female mosquitoes.
  6. Site near vegetation or at the bases of larger trees. Avoid areas that get a lot of direct sunlight.
  7. Set up a reminder on your phone to add more Mosquito Dunks. NB: if you forget, the buckets will be generating mosquitoes.
  8. If you’re traveling for more than three weeks during the summer, dump out all your buckets and start over when you return.
  9. Purge your yard of all other objects that might retain stagnant water so that mosquitoes are forced to leave their eggs in the trap.
  10. Make some for your neighbors, especially those who are spraying pyrethroids.
  11. Get local folks on board by writing a letter to your local paper (e.g., here’s my March 2026 blurb in The Swarthmorean). The more people who use these traps the better.

Are they working?

To determine whether mosquitoes are ovipositing, just look for egg rafts on the surface of the water (photo below, left). You can also check for eggs of Asian tiger mosquitoes (Aedes albopictus) which are oviposited singly or in small groupings on the edges of the container, above the waterline, or on pieces of wood that are floating on the surface (photo below, right). If there are eggs and no larvae, the Bti is doing its thing. If you see larvae in the water, they are not working — if that’s the case, dump everything and start over or add some fast-acting Mosquito Bits (kills in minutes, just as safe) along with a fresh chunk of Mosquito Dunk. Here‘s a great photo on Reddit with several thousand first-instar larvae swimming happily with a non-functioning Mosquito Dunk. If you don’t trust yourself to ID larvae, send me a pic or tag me on social media.

Female Asian tiger mosquito (Aedes albopictus) with larvae and eggs

Safety

Bti toxins are completely nontoxic to mammals, birds, and all insects except mosquitoes, black flies, and fungus gnats. For an excellent overview of the mode of action and safety, please see this report (PDF).

Sources of Bti

The instructions above mention Mosquito Dunks but there are other products that contain live Bti. Just search for any of the following: Biosolutions Bactive, Bonide Mosquito Beater Water Soluble Pouches, Bactimos mosquito dunks, Terro Mosquito Larvacide Pouches, VectoBac Water Dispersible Granules.

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