Tree Fruit Insect Pests - Yellow Jackets and Hornets

While greater opportunities for biological control of some apple pests exist in today's orchards, we are seeing a greater diversity of generalist predators.
Tree Fruit Insect Pests - Yellow Jackets and Hornets - Articles
Tree Fruit Insect Pests - Yellow Jackets and Hornets

Implementation of the Food Quality Protection Act (FQPA) expedited the registration of reduced-risk pesticides that are safer to the agricultural produce consumers, farm workers, and the environment. Many of the newer insecticides being used in fruit orchards currently are often more selective in their activity towards specific types of insects. Broad-spectrum products that were the mainstays of pest control in orchards since the 1960s, have been eliminated from use or so heavily restricted by longer worker re-entry periods and pre-harvest intervals that use is greatly restricted. FQPA has led to over 30 new insecticide/miticide active ingredients being registered in tree fruit since the late 1990's. The shift to more selective pesticides has complicated orchard pest control in many ways for fruit growers. While greater opportunities for biological control of some apple pests exist (e.g., biological mite control with the predatory mite, Typhlodromus pyri, or spirea aphid control with the Asian lady beetle) and we are seeing a greater diversity of generalist predators, there has also been a resurgence of some pests such as plum curculio, woolly apple aphid, San Jose Scale and European apple sawfly that were incidentally controlled with applications of broad-spectrum insecticides for primary pests such as codling moth. We have also noticed increases of nuisance pests such as ticks, deerflies and mosquitoes in orchards as broad-spectrum insecticide use declined.

The most dangerous resurgence directly affecting humans has to be that of increased numbers of hornets and yellow jackets. While they are generally beneficial predatory insects that feed on a variety of pests early- to mid-season, their tastes shift from protein to sugars in the fall and they can become pests feeding on injured or ripe fruit. The biggest problem, however, comes from dangerous stings to farm workers and to the public in U-Pick and farm market operations. We have five types of yellowjackets in Pennsylvania fruit orchards: the Eastern Yellowjacket (Vespula maculifrons), the German Yellowjacket (Vespula germanica), the Southern Yellow Jacket (Vespula squamosa), the Common Yellowjacket (Vespula vulgaris), and the Bald-Faced Hornet (Dolichovespula maculata), which is actually an unusually large black and white yellowjacket. Strangely enough, the Pennsylvania Yellowjacket (Vespula pennsylvanica) is not found in Pennsylvania, but only in the mid-west and western states. For all of the species except the Bald-Faced Hornet, the names matter little, since the biology is very similar amongst most species, and the only significant difference between species is nest size. Considered to be among the most aggressive of all wasps in our area, yellowjacket numbers are also immense by late season with over 5,000 individuals in a single nest.

The Bald-Face Hornet is the only species that nests in the orchards, with all other yellowjacket species nesting mostly in the ground or buildings and flying into orchards from the edges. The Bald-Faced Hornet is thus most problematic to fruit pickers because its large, oval to football shaped paper nests are attached to limbs and often hidden by leaves. Significantly less aggressive than the smaller ground nesting yellowjackets, the larger Bald-Faced Hornet is much more docile when feeding than the other yellowjacket species. They will, however, vigorously defend their nests when it is disturbed by ladders or hands reaching for fruit. The more aggressive nature of the other ground nesting yellowjacket still causes problems for fruit pickers that disturb them feeding on injured or fallen fruit.

Our only true hornet is the European Hornet (Vespa crabro), which was introduced into New York in the mid-1800s and has since spread to most of the eastern U.S. The 1.5 to 2 inch size of this wasp is very intimidating to most people and it most closely resembles the cicada killer wasps in our area. Despite being 3 to 4 times larger than worker yellowjackets, it is generally quite docile away from its nest and will back away from trouble if given a chance. Despite its size, its sting is apparently no worse than the smaller yellowjackets. It is a very good predator with numerous videos on the internet of it preying on large insects such as cicadas and grasshoppers. Like the yellowjackets, however, its tastes switch to sweet foods such as fruit and the sap from trees in the fall, and it can quickly reduce ripe and injured fruit to the core with its massive mandibles as seen in the pictures below by fruit grower, Paul Huffman, of Northumberland County. Most homeowners see them coming to lilac and other shrubs in the fall where they girdle twigs to feed on the sap and can cause serious injury to or even kill bushes. Primarily a forest species nesting in hollow trees, it also flies in from outside the orchards and often from long distances. It will also nest in houses or buildings if given the chance, often under the vinyl siding of houses. The nests of the European Hornet are most easily distinguished from yellowjackets and the Bald-Faced "Hornet" in that the nest is made of a brown paper rather than grayish-silver of the other species and it prefers to have its nests mostly hidden rather than exposed to light. Males of this wasp are unusual in that they will come to lights at nights. Many other wasps known as paper wasps or mud-daubers look similar to yellowjackets and hornets, but are mainly predators and pollinators with smaller nests that look like upside down umbrellas. They are usually less aggressive than yellowjackets and hornets.

Homeowner control products for both species, generally consist of pyrethroids and penetrants for quick knockdown, but are expensive and impractical for control in orchards except on a limited basis. The use of even a single pyrethroid spray after bloom would also most likely kill predatory mites and flare populations of pest mites. Hornets and yellow jackets, however, overwinter only as queens in Pennsylvania, with the rest of the colony dying in the fall with the advent of heavy frosts. Killing these queens in the spring, when they are just starting to build nests would be much easier than killing them in the fall when the nests are much bigger, better protected, and when they consist of several thousand individuals. Timing of a single broad-spectrum insecticide spray at a critical time (unknown currently and may vary with species) may be key to reducing populations or the use. The use of traps baited with fish or other meat early season may also be effective. Many commercial traps exist for homeowners using meat, sugar or pheromones as bait, but many are more effective at making homeowners feel like they are getting revenge rather than reducing populations quickly. Many of these traps are also expensive and too time consuming to bait and replace for fruit growers to use on a large scale.

Safety

About 50 to 100 people die in the US due to yellowjacket/hornet stings with most of these deaths from the 0.5 to 1.0% of folks that have a hypersensitive reaction to even a single stings. To a non-sensitive person, depending on size, age, and general health, death can occur in adults after about 1,500 stings. Since yellowjackets release an alarm pheromone when aggravated or squashed that attracts other yellowjackets, attacks near nests can easily lead to attacks by these high numbers. Unlike the honey bee that can only sting once and dies soon after, yellowjackets/hornets have smooth stingers than can sting repeatedly as well as bite without dying. Smaller children are more sensitive and deaths have occurred with only 300-400 stings. Most reactions occur within several hours of the sting, but some may occur over several days. Fast, jerky movements are more likely to cause attacks, so remaining still and then slowly moving away from wasps is recommended. Heavy clothing will give some protection as well.

First Aid

  1. If a sting occurs in the mouth or throat - apply ice and get medical help immediately since swelling in these areas can lead to suffocation.
  2. Hypersensitive people require special attention. Some are allergic to bee stings, but not to wasps since the proteins are different. The reverse is also true. People who experience other severe allergies and hayfever are more likely to be sensitive. Anyone who experiences dizziness, respiratory reactions and color changes due to a sting should be taken in for treatment immediately. Other symptoms include fever, chills, hives, joint and muscle pain and swelling of the lymph glands or throat. A severe case may include a sudden drop in blood pressure and fainting. An antihistamine such as Benedryl, can slow symptoms if taken immediately as do syringes of epinephrine (EpiPens). These treatments only delay symptoms in sensitive people and are not substitutes for medical treatment.
  3. All others - non-allergic reactions to stings include pain, itching, redness and swelling for up to two days after treatment. Wash the area around the sting and apply antiseptic. Washing can remove some of the venom and thus reduce pain and swelling. Unlike honey bee stings, yellowjacket/hornet stingers are smooth and can sting repeatedly. There is no stinger left behind that can be scraped away before all the venom is injected like with honey bees. Apply ice or commercial products to relieve pain and an alternative is a paste of meat tenderizer and water which can break down the venom and reduce pain and swelling. Antihistamines can also offer some relief from pain and swelling. After treatment the victim should rest since strenuous activity can move the venom more quickly through the body.


Feeding damage caused by European Hornet and possibly other wasps on apples. (Photo courtesy of Paul Huffman, Fruit Grower)


Feeding damage caused by European Hornet pear fruits. (Photo courtesy of Paul Huffman, Fruit Grower)


European Hornet feeding on a pear fruit. (Photo courtesy of Paul Huffman, Fruit Grower)

Prepared by David Biddinger, Penn State Entomologist and Neelendra Joshi, former research technician.