The Four Month Trap
Fight Dengue and Zika with The Four Month Trap Shared with permission from Van Eden from Hawaii Dengue Awareness.
Most mosquito traps, including the commercial TrapNKill, need frequent replacement or refreshing. This new experimental design uses a three or five gallon bucket and lasts four months – the only maintenance is to check the water level once a week.
It is based on two key research papers on long lasting insecticides. The first shows that a pyrethroid called bifenthrin used on the landing strip does not diminish in efficacy after four weeks in the field; the second shows that an “organic” pesticide called spinosad used in the water bath continues to kill larvae even after 20 weeks.
By using these chemicals, we expect these traps will last 4 months, with the only maintenance being to check the water level periodically. However, if you find openings obstructed by leaves or other debris, or by spider webs, you should check more frequently.
There are trade-offs: the poisons last longer in the environment so you must take extra care with preparation and disposal. If done correctly, none of these chemicals need to get into the environment – they remain in the bucket until we dispose of them.
The landing sticks (BIF sticks) are a bit complicated to make, and it is best to make a few hundred at once – a great community project. More instructions for making BIF sticks are here.
You need to check these traps at least every two or three weeks (more frequently in hot weather). A quick peek through the opening should be enough. Check:
- The water level is correct
- No animals or foreign objects are inside
- The landing strip is intact
- The landing strip is NOT covered in mold or fungus. (This is a common failure mode in some areas.)
The landing pad poison: Bifenthrin.
Commercial products include Telstar Pro and Bifen. They are liquids with a concentration of 7.9% bifenthrin and must be diluted before use. Bifenthrin is approved for use in kitchens and food handling areas.
The water bath poison: Spinosad.
There are several commercial formulations, such as Monterey Garden Insect Spray with Spinosad, or Bonide 252 Dead Bug Concentrate. These instructions assume 0.5% concentration of spinosad.
Spinosad is approved for use on organic produce up to the day before harvest.
The Fact sheet is here.
Here’s what you need:
- Bifenthrin, 7.9% concentration.
- Spinosad, 0.5% concentration.
- Smooth walled 3 or 5 gallon bucket. Smaller containers are not appropriate, and a lid is important to keep things out and reduce evaporation. Spray paint black if needed. Do not allow paint inside the bucket.
- A tight fitting lid.
- One or more wood strips, approximately 1″ wide, 0.125″ thick, and long enough to reach diagonally from the bottom of the bucket to just under the rim. Paint stirring sticks or wood shims from the hardware store work well.
- A place on which to dry the landing pad sticks after painting with bifenthrin. A few 2x4s laid on sawhorses or the ground work fine.
- A pinch of compost or some pond water or compost tea.
- A teaspoon and 8 fluid ounce cup for measuring liquids. Do not use utensils you will later use for food. Six teaspoons is one fluid ounce.
- A small disposable paint brush used to brush the bifenthrin solution onto the sticks.
Here’s what you do:
- Write “BIF” on one the end of the wood strips, and a line about 1 inch down. You will keep this end clear of bifenthrin.
- Prepare a 1% solution of bifenthrin by putting 1 ounce (6 teaspoons) of the concentrate in the 8 ounce cup (shake container very vigorously first). (Highly recommended: add one or two tablespoons of red dye. This helps you recognize the strips have been treated after they are dry.) Add water to make the solution up to 8 ounces total volume.
- Lay the strips flat on the surface you have prepared. Using the paintbrush, wet the wood strips with the diluted Talstar solution, taking care not to get the end with the line wet. Don’t drip dry, just leave horizontal until dry. Turn over and paint the other side, and let it dry. Once they are completely dry, you can use them, or store them in a sealed, labeled container.
- Add one gallon (for a 3 gal bucket) or two gallons (5 gal bucket) of water to your container. Pond water is great.
- For each gallon of water you added, add 0.5 ounces (3 teaspoons) of Spinosad (shake container first), to make a 20 ppm dilution.
- If not using pond water, add a pinch (1 teaspoon) of compost or some compost tea, the smellier the better.
- Take the lid, and cut four or more 3 inch diameter holes or squares. Using smaller holes helps prevent animals (cats, dogs) getting in. If you use smaller holes, make more of them.
- Write the date on the clean end of the dried landing stick, and place into the bucket with the clean end up. You do not need to wet it more than letting it touch the water. You can use two or three.
- Press the lid firmly over the bucket, trapping the landing sticks(s) in place.
- Place in a shaded location out of the rain. Sunlight degrades the chemicals used.
- Maintain a written record of where and when you placed the traps.
- Clean up, ensuring any bifenthrin contaminated materials are put in the garbage, or cleaned well. Do not burn bifenthrin containing garbage.
Dispose the wood strips in the garbage. Do not burn them. Dispose the water on the ground away from ponds or streams, where the spinosad will break down quickly in soil.
Wood strips are used instead of paper because paper will breakdown over the 4 month lifetime of these traps.
These instructions are based on the measured absorbency of wood stirring sticks, about 0.01g/cm^2. The dilution of the concentrate is chosen so that in the end, the concentration of bifenthrin is about 0.1mg per cm^2, or around 20 mg per stick.