February 25, 2018

Yellowjackets

Suzanne Wold-Burkness, Department of Entomology, University of Minnesota

Yellowjackets, Vespula spp., (Hymenoptera: Vespidae) are actually considered a beneficial insect because they pollinate plants and prey upon insects that are identified as pests.  However, in late summer and early fall when their populations peak, the diet of the yellow jacket changes from insects to sugar sources such as grapes.  Feeding causes damage to the grapes.  Addtionally, yellowjackets pose a stinging hazard in the vineyard to the people harvesting the grapes.

Identification

Yellowjacket on a grape cluster (E.C. Burknss & T.L. Galvan, U of MN

Yellowjacket on a grape cluster (E.C. Burknss & T.L. Galvan, U of MN

 

The yellowjacket is about 1.3 cm long and has alternating yellow and black bands on the abdomen.

Foraging yellow jackets are often mistaken for honeybees because of their similar appearance and the fact that they are sometimes attracted to the same food source.  Honeybees are slightly larger than yellow jackets and are covered with setae which are mostly absent on yellow jackets.  Foraging honey bees can be identified by the pollen baskets on the rear legs that are often loaded with a ball of yellow or green pollen.  The yellow jacket has a smooth stinger that can be used to sting multiple times, whereas the honey bee has a barbed stinger than can be used to sting only once.

Biology & Life Cycle

Yellow jackets are social insects that have a colony division of labor between undeveloped female workers, males and fully developed female queens.  Newly mated queens are the only members of the colony that overwinter.  In spring, the overwintered queen emerges and begins the establishment of a nest which is normally located in a soil cavity such as an abandoned mouse nest or hollow tree.  Other possible nest sites are in buildings, including attics, porches, eaves or sheds.

The queen builds a small paper nest and lays several eggs which hatch and mature in to adult workers.  This first generation of infertile workers undertakes all tasks of nest expansion including foraging for food, defending the colony entrance and feeding the queen and larvae.  The colony rapidly increases in size and the number of adult yellowjackets within each colony may reach several hundred by August.

Nests are constructed of several layers of comb made of tiny bits of wood fiber chewed into paper-like pulp.  During this peak population period, the colony produces “reproductive cells” that mature and provide future queens and reproductive males that eventually leave the nest for mating flights.  Mated queens fall to the ground and seek out a protected overwintering place such as a brush pile, a hollow tree or a building.  Males do not overwinter and die after they have successfully mated.

Damage

Yellowjacket feeding on an injured grape (E.C. Burkness & T.L. Galvan, U of MN)

Yellowjacket feeding on an injured grape (E.C. Burkness & T.L. Galvan, U of MN)

Yellowjackets feed on ripe grapes in late summer and early fall, damaging the crop. They also may be a danger and annoyance to pickers.

Management

Cultural Control

Harvest the grape clusters as soon as they ripen to discourage yellowjacket feeding.  Remove any overripe or damaged fruit from the vineyard area.  In addition, do not leave any food items near the vineyard, as they may attract yellowjackets to the area.

Trapping

Traps containing n-heptyl butyrate which mimics the odor of fruit. can be used outside the perimeter of the planting to discourage yellowjackets from feeding on grapes. Place traps before the berries begin to ripen. Place traps early (July or early August) to improve chances of success. Once the yellowjackets find the ripened fruit, the traps will be of little benefit.

Chemical Control

It is not an effective management option to use an insecticide.


References

Dami, I., B. Bordelon, D.C. Ferree, M. Brouwn, M.A. Ellis, R. N. Williams, and D. Doohan.  2005.  Midwest Grape Production Guide.  The Ohio State University Extension Service.  155 pp.

Ellis, M. D. Doohan, B. Bordelon, C. Welty, R. Williams, R. Funt, and M. Brown.  2004. Midwest Small Fruit Pest Management Handbook.  The Ohio State University Extension. 125-129.  http://ohioline.osu.edu/b861/

Lyon, W. F. Yellowjacket.  Ohio State University Fact Sheet.  http://ohioline.osu.edu/hyg-fact/2000/2075.html

Minnesota Grape Growers Association.  1999.  Growing Grapes in Minnesota.  MN Grape Growers Association, Lake City, MN.

 

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