WSU Whatcom County Extension

Integrated Pest Management for Blueberries

Yellowjacket and Paper Wasp

(Vespula pensylvanica, V. germanica, V. vulgaris, and Polistes dominulus)

Insects & Invertebrates

 

Yellowjacket

Symptoms

Yellowjackets and paper wasps are not considered direct pests of blueberry crops, but are considered beneficial insects because they feed their young numerous insects that normally damage crops. They also predate on numerous fly species that are common household and farm pests. Populations can cycle from low numbers to higher levels by year. During years of large populations, yellowjackets can become dangerous to blueberry workers during cultivation and harvesting. In the past, some growers have left whole sections of their fields untouched because of the danger to pickers when wasp populations were severe. The potential for loss of yield where nests have been present is a painful reality.

 

Identification

Yellowjackets have black and yellow striped coloring on the abdomen and are about 1/2 inch long. Their bodies are not covered in hair as are honeybees, but they may appear similar from a distance. Paper wasps are about 3/4 inch long and have a more slender body than the yellowjacket.

 

Life History

Annual colonies of yellowjackets and paper wasps occur in the Pacific Northwest. The inseminated queens are the only members of the colony to overwinter. These females find protected locations such as under bark and in stumps and logs to spend the winter. Queens emerge during the first warm spell in the spring sometimes as early as the end of March. They select a nesting site and build a small nest in which they lay eggs. When the eggs hatch, the queen will feed the larvae for approximately three weeks. Larvae pupate, and emerge as smaller, infertile females called workers. These workers take over the rearing responsibilities of the larvae and the queen then rarely leaves the nest. The colony quickly grows, reaching maximum size in August and September and, depending on the species, can consist of as many as 5,000 workers and 15,000 cells. It is at this time when many yellow jacket colonies become pestiferous.

In the fall, new males and queens are produced, emerge and mate. After mating, the males soon die and the inseminated queens seek a sheltered place to overwinter, thus starting the cycle over again. Old nests are not re-used and quickly disintegrate during the winter weather. Nests may be constructed underground or attached to a plant or other structure.

 

Monitoring

Aerial nests are more easily seen and managed. During regular monitoring keep an eye open for small nests being developed and return after dark to remove them. It is easier to remove a small nest than a large one. Underground nests are almost impossible to locate and exterminate in a field setting, although it is possible to search for them at night.

 

Thresholds and Management

Yellowjacket traps are available and can be used to draw the wasps away from human activities. There are a number of different types of traps and lures available; chemical commercial lures or traps baited with soft drinks or fruit juices. Other traps are hung and baited with meat, poultry, or fish. The bait must be fresh, as the wasps are not drawn to rotting flesh.

Aerial nests are easily controlled using some of the newer aerosol products that can propel the insecticide up to 20 feet. Apply in the evening after most of the foraging workers have returned to the nest. Direct the stream into the hole of the nest and thoroughly wet the entire nest. Leave the nest a day or two so that the residue will kill any late returning workers. Always spray and remove aerial nests during the coolest part of the evening and cover yourself with thick clothing and wear glasses. For underground nests use registered hornet and wasp spray and direct the insecticide into the entrance hole after dark. After treating, do not seal the entrance as late returning foragers will enter the nest and be killed by the residue.

Remember, yellowjackets and paper wasps are beneficial insects – control them only if absolutely necessary.

 

Resources

WSU Extension Bulletin 0643; Yellowjackets and Paperwasps
http://cru.cahe.wsu.edu/CEPublications/eb0643/eb0643PrinterFriendly.pdf

WSU Extension; European Paperwasp
http://www.puyallup.wsu.edu/plantclinic/resources/pdf/pls13europeanpaperwasp.pdf

WSU Extension Fact Sheet FS017E; Protecting Honeybees against Yellowjackets
http://cru.cahe.wsu.edu/CEPublications/FS017E/FS017E.pdf

WSU Whatcom County Extension; European Paperwasp
http://whatcom.wsu.edu/ag/homehort/pest/p_dominulus.htm

 

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WSU Whatcom County Extension • 1000 N. Forest St., Bellingham, WA 98225 • (360) 778-5800 • whatcom@wsu.edu