The Right Trap for the Right Wasp Diane Alston, Extension Entomologist Utah State University Extension
A common question I hear this time of year is, "My yard is overrun with wasps, and they are eating my raspberries and grapes. I put out a trap, but why hasn't it helped?"
The most likely reason is that the trap you are using is not attractive to the target wasp species. Since the invasion of the European paper wasp to Utah less than 10 years ago, this species has become a prominent nuisance and fruit eating pest for growers and home gardeners.
The primary type of wasp trap sold in garden and home centers contains heptyl butyrate, a chemical that is attractive to the yellow jacket wasp, but not to the European paper wasp.
Dr. Peter Landolt, USDA ARS Entomologist in Wapato, WA, studies the chemical ecology of insects, and has developed do-it-yourself traps to attract food eating social wasps. The key is first determining the problem wasp species, and then selecting an appropriate trap.
The European yellow jacket has a broad "waist" and more yellow than black color on its lower body (abdomen). It commonly builds its paper nests in the ground or under dense vegetation. Yellow jackets are primarily attracted to meat baits. A simple trap can be made by cutting the top from a plastic soda bottle and inverting it (without the lid) into the bottom "cup."
Punch a hole on each side of the cup and hang the trap using wire or twine. Hang a piece of meat, such as hamburger or fish, just below the funnel-shaped top and fill the cup with water plus 1 tsp. detergent. Position the meat so that the wasp will fall into the soapy water when it attempts to fly away after cutting off a piece.
The European paper wasp has a narrow waist and more black than yellow on its abdomen. This wasp builds upside-down umbrella-shaped paper nests and attaches them to overhangs, decks, and other structures.
The European paper wasp is highly attracted to decaying fruit. Landolt recommends loading the soda bottle trap previously described with a mixture of 1 part fruit juice to 10 parts water + 1 tsp. liquid detergent. The juice must begin to ferment in order to be attractive, and so it may take a day or two for rapid fermentation to begin.
You can accelerate the fermentation by adding a piece of overripe fruit. The wasps will try to fly up towards the light after getting a bite of food, but will hit the bottom of the funnel and fall into the soapy water which will make it difficult for them to fly. They should eventually get caught in the liquid in the bottom of the trap. Landolt cautioned against adding insecticides because the sweet traps could attract and harm honeybees.
Since ripe and overripe fruits will compete with traps for the wasps' attention, he advised to trap wasps preemptively to reduce populations before they become a problem during fruit harvest. He advised positioning traps every 30 ft around the perimeter of a vineyard or orchard as well as within the field.
The higher the wasp population, the more traps will be required to reduce wasp numbers. The traps should be checked regularly to remove dead wasps and refill the bait. If you need assistance with identifying a wasp, collect and submit a sample to the Utah Plant Pest Diagnostic Lab.
Check this address for more information, pictures of the insect and the trap.