Beginner

Scientific Name
         Vespula spp.

Identification
Adults

• 1.3 cm long
• alternating yellow and black bands on the hairless body

Injury

• Produce slits about 0.2 mm long in the berry skin with their mouthparts
• Sap leaks from berry
• Prolonged feeding results in multiple wounds and eventual mining of a cavity extending into the internal tissues of the berry

Often Confused With
Honey Bees- slightly larger than wasps, are brown and black, and are covered with hairs.

Period of Activity
Pre-harvest.

Scouting Notes
Usually associated with ripe fruit, especially when it is injured.

Threshold
None.

Advanced

Scientific Name
         Vespula spp.

Identification
Adults

• 1.3 cm long
• alternating yellow and black bands on the hairless body

Injury

• Produce slits about 0.2 mm long in the berry skin with their mouthparts
• Sap leaks from berry
• Prolonged feeding results in multiple wounds and eventual mining of a cavity extending into the internal tissues of the berry

Often Confused With
Honey Bees- slightly larger than wasps, are brown and black, and are covered with hairs.

Biology
Wasps are social insects. They live in colonies consisting of a queen, female workers and males. Each colony starts out the year with a single, mated female queen, the only life stage that is able to survive the winter. In the spring, the queen emerges from a protected site and begins the process of nest building. She constructs her papery nest out of wood fibres and lays several dozen eggs. The larvae mature and become infertile females, which continue the work of expanding the nest, foraging for the colony’s food, and defending the colony. The queen continues to lay eggs and expand the numbers of yellow jackets, never leaving the nest again.

Once the colony reaches a size of up thousands of individuals, some of the eggs that are laid develop into what will become future reproductive queens and males. Future queens and males leave the colony to mate late in the fall. The mated females seek out places to stay alive during the cold months. The original colony dies and the papery nest falls apart.

Wasps prey on insect pests -especially caterpillars in fruit crops - during the spring and early summer. At that time of year queens, and later their offspring, collect protein (caterpillars, scavenged flesh from dead animals, etc.) to feed their developing young or nest-mates. In late summer, wasps become agricultural pests when their food preferences change from meat to sugar sources such as ripening grape berries. They feed on ripe and damaged berries and are occasionally present in such large numbers as to seriously affect yield. In other cases they are just a nuisance when mechanically harvesting. However, for hand harvesting, wasps can be a dangerous and disruptive pest for workers.

Period of Activity
Pre-harvest.

Scouting Notes
Usually associated with ripe fruit, especially when it is injured.

Threshold
None.

Management Notes
Minimize injury to grapes caused by birds, grape berry moth, powdery mildew and bunch rots as well as berry squeeze in tight clustered thin varieties. Grape clusters should be picked as soon as they ripen to discourage wasp feeding. Remove any overripe or damaged fruit from the grapevines. Insecticides are not an effective management option for controlling wasps.

Trapping wasps later in the season may help lower the damage on grapes but the trapping needs to be started early and maintained through harvest. Trapping will not eliminate all wasps in the area - it will only lessen the problem. Commercial traps are available at any hardware store. Early season bait should be fresh meat or fish but later in August, sweet liquids are best. Commercial liquid baits do work, but recent research showed that Mountain Dew(tm) was the best attractant over orange soda or commercial bait. Jam, honey, molasses, yeast mixtures, and even beer have also been used as wasp bait with varying degrees of success. When yellow jackets are plentiful, just about any sweet liquid will attract dozens to funnel traps each hour so the traps need to be serviced daily or they will lose effectiveness when full of dead wasps.