Managing Mosquitoes Around Your Home

Go to http://mosquitosafari.tamu.edu/ or En Español  

Mosquito Dunks

Effective mosquito management requires personal responsibility.

• Drain any and all standing water on your property. 
• Don’t forget to check places you normally don’t see, such as clogged gutters, leaking irrigation lines, downspout runoff tubes, etc.! 
• Dump and refill birdbaths, plant saucers, and pet bowls twice a week to prevent mosquito breeding. 
• For water tanks, ponds, or troughs that are not easily drained and refilled, the use of mosquito dunks are a cheap, safe, and easy option.

Mosquitoes have always been an annoying and sometimes deadly aspect of summer, and with the recent spread of West Nile virus there has been a heightened interest in mosquito control throughout the United States. Homeowners, ranchers and farmers looking for a safe, nontoxic way to control mosquitoes can use Mosquito Dunks, which kill mosquitoes before they can become flying, biting, disease-carrying adults.

What is a Mosquito Dunk?
A Mosquito Dunk looks like a small, beige donut which floats on standing water. As the Dunk slowly dissolves, it releases a bacterium which is toxic to all species of mosquito larvae.

What is the active ingredient in Mosquito Dunks?
The active ingredient in Mosquito Dunks is Bacillus thuringiensis subspecies israelensis. (B.t.i.). B.t.i. is a bacterium that is deadly to mosquito larvae but harmless to other living things.

Where should Mosquito Dunks be used?
Just float a biodegradable Mosquito Dunk in water troughs, koi ponds, birdbaths, rain barrels or any place where water collects and remains for periods of time. When female mosquitoes lay their eggs in standing water treated with a Mosquito Dunk, the larvae will hatch and begin to eat the B.t.i. The B.t.i. will kill the mosquito larvae before they can grow up to become biting and disease-spreading adults.

How do Mosquito Dunks work?
While floating, a Mosquito Dunk slowly releases a long-term biological mosquito larvicide at the water’s surface. This larvicide gradually settles in the water, and while it travels through the water it is eaten by the mosquito larvae growing there.

What kinds of mosquito larvae will a Mosquito Dunk kill? 
There are approximately 2,500 species of mosquitoes throughout the world. The B.t.i. in Mosquito Dunks will kill the larvae of ALL SPECIES of mosquitoes.

How much water will one Dunk effectively treat?
One Mosquito Dunk will effectively treat 100 square feet of surface water for 30 days or more. For less water, a portion of a Mosquito Dunk can be used. Suitable treatment sites include swamps, fragmented puddles, trash dumps containing water, or water with a high concentration of organic material.

Are Mosquito Dunks safe to use around fish, birds, wildlife, pets and children?
Yes. B.t.i., the active ingredient in Mosquito Dunks, is very target specific for mosquitoes and does not adversely affect other organisms in the water. Mosquito Dunks are also safe for use around birds, wildlife, children and pets. The EPA has registered Mosquito Dunks for use in animal watering troughs and fish habitats. More recently the Dunks have been approved for use Organic Production and Gardening, under the National Organic Program guidelines.

What if my dog eats a Mosquito Dunk?
Don’t worry. Even if your dog eats an entire Mosquito Dunk, this will not adversely affect the animal. If an animal eats a Mosquito Dunk or drinks water treated with a Mosquito Dunk, it essentially gets a large dose of protein and calcium. The Dunks are labeled for application to livestock watering troughs.

What is the shelf life of Mosquito Dunks?
Mosquito Dunks can be stored indefinitely because, technically speaking, the dried B.t.i. in Mosquito Dunks is not living, viable bacteria. (The toxicant that kills mosquito larvae is actually part of the B.t.i. spore). Government Mosquito Control programs have
conducted field tests where Mosquito Dunks of eight years age were effective at killing mosquito larvae at close to equal rate as new product. Additionally, alternate wetting and drying will not reduce the effectiveness of Mosquito Dunks.

Will storage temperatures affect the viability of Mosquito Dunks?
The best storage condition for Mosquito Dunks is a cool, well-ventilated place. Because B.t.i. is a bacterium, extreme cold or even freezing temperatures will not reduce the effectiveness of Mosquito Dunks. However, prolonged exposure (more than 24 consecutive hours) to temperatures above 100 degrees F. may affect the efficacy of the product.

Online Resources:

• Williamson County - West Nile Virus Surveillance Information
• CDC - West Nile Virus Information
• Texas Dept. of State Health Services- West Nile Virus InformationFrequently Asked Questions
• Texas A & M AgriLife Extension - Texas A & M AgriLife Extention West Nile Virus Resources
• Texas A & M AgriLife Extension - Mosquito Control Videos
• Centers for Disease Control and Prevention Fact Sheets
• Children’s Page (Fun and Learning)

For more information about Mosquito Management initiatives in Williamson County contact Environmental Health Services at 512-943-3622.