Ministry of Agriculture
Grape Insect and Mite Pests
Wasps
- Identification
- Life Cycle and Damage
- Monitoring and Spray Thresholds
- Biological Control
- Cultural Control
- Chemical Control
Prepared by D. Thomas Lowery, Agriculture and Agri-Food Canada, Pacific Agri-Food Research Centre, Summerland.
A number of species of yellowjacket wasps (Hymenoptera: Vespidae) are pests of grape; the most numerous and troublesome being Vespa pennsylvanica (Saussure). Two uncommon species of paper wasp (Polistes sp.) are native to our area. The European paper wasp, P. dominulus, was found in British Columbia in 2003 and has since become very common, particularly around buildings. Yellowjackets, hornets and paper wasps are important predators of grape pests throughout most of the year, but in fall they often feed in large numbers on damaged fruit. Wasps are also an annoyance to vineyard workers and to pickers during harvest operations. Paper wasps are less aggressive than yellowjackets or hornets and are not as prone to sting.
Identification
Yellowjacket workers are about 1.5 cm in length; the abdomen appears largely yellow with thin black bands. Hornets are slightly larger and appear largely black with yellow or white bands. Paper wasps have thinner bodies with a more pronounced constriction (stalk) between the thorax and abdomen. The body is dark with some yellow markings, but they appear reddish-brown due to the colour of the wings and distal parts of the legs. In flight the legs of paper wasps dangle visibly below the body. All of these wasps produce paper nests, but the brood cells of paper wasps are exposed.
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| European paper wasp | European paper wasp nest in an ornamental shrub |
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| Wasp feeding on grapes. Photo courtesy John Vielvoye, Kelowna B.C. |
Wasp damage to grapes. Photo courtesy John Vielvoye, Kelowna B.C. |
Life Cycle and Damage
Yellowjackets and paper wasps overwinter as fertilized females in sheltered locations. These queens seek suitable nest sites in spring and establish a new colony. Nests are initially small, consisting of only a few paper cells, but as workers develop they assist in building up colony numbers and the size of the nest. Depending partly on the species, nests can be in the ground, under the eaves of houses, in hollow trees or the walls of buildings, or exposed in trees. In fall, in addition to workers, colonies produce both males (drones) and queens. When freezing weather arrives, all the drones and workers, as well as the undeveloped larvae and pupae are killed.
Wasps prey on other insects, scavenge food and feed on nectar and the juices of fruit. It has been reported that wasps do not damage fruit themselves but take advantage of injury caused by other insects or birds, diseases such as sour rot, or splitting of fruit. There are contrary reports, however, particularly relating to the European paper wasp, that they are able to directly feed on intact fruit. As mentioned above, the greatest detriment is from annoyance or injury to pickers. Their stings result in swelling and a painful itch and can trigger severe allergic reactions in some individuals.
Monitoring and Spray Thresholds
Wasps are generally considered to be beneficial or of little economic importance. There are no established thresholds and the need to spray is determined by the tolerance level of individual vineyard managers. The recent arrival of the European paper wasp will likely make it necessary to control wasps more frequently.
Biological Control
Wasp colonies can be attacked by other wasps. Eastern and western kingbirds feed on foraging adults and larvae are subject to certain diseases. The onset of winter eliminates established colonies and overwintering queens often succumb to cold or are eaten by other insects, or even by mice.
Cultural Control
Elimination of nests early in the season can be an effective management strategy, but they are often located outside the vineyard or well hidden. Aerial nests in trees or under eaves can be removed and placed in a plastic bag at night when wasps are inactive. Nests in walls or natural cavities can be treated by blowing or puffing commercial wasp control products into the entrance holes at night. Sealing of entrances can help prevent future nests.
Trapping can be used to reduce numbers of foraging wasps in localized areas. Commercial wasp traps are available, or homemade versions can be made from recycled 1 litre plastic pop bottles. Sugary solutions are contained in the bottom of the trap and wasps that enter the small holes eventually fall into the liquid solution and drown.
Trapping early in the season when populations are low is generally more effective than attempting to remove large numbers of wasps later in the season. For additional information on social wasps, management strategies, and design of wasp traps, visit the University of California Statewide Integrated Pest Management Program.
Chemical Control
There are currently no insecticides registered specifically for the control of wasps feeding on grapes.
September 2010
