As late summer turns to fall, perhaps the most predictable visitor to the myriad outdoor fairs and festivals, as well as residential patios and outdoor dining areas, is the yellow jacket (Vespula spp.)
Considered the most dangerous of the wasp species due to its aggressive behavior while foraging and its distinct preference for human foods, yellow jackets present, at best, an annoyance, at worst, a public health threat. Each year, stings account for more than 100,000 emergency room visits and several deaths from allergic reactions.
Control of yellow jackets is accomplished through nest elimination and/or trapping. Yellow jackets tend to nest in ground voids, such as old rodent burrows, and in voids in walls and ceilings. When treating nests, it is safest to treat at night, when the majority of workers will be in the nest, and to wear protective clothing. Nests have a single entry and an appropriately labeled liquid or aerosol insecticide should be injected directly into the nest. The area around the outside of the entryway also can be dusted prior to nest treatment. It is best to cover the hole if possible until the following day.
One practice gaining in popularity for nest treatments is foaming. Compared to liquid treatments, foam hangs on the nest longer, and has the effect of immobilizing and smothering the insects, resulting in less sting potential. Some pest professionals foam insecticide, while others simply use foaming agent alone and find that to be effective in a manner similar to insecticidal soap. This is an excellent option for sensitive or “green” accounts. Nests in structures should be removed a few weeks after treatment is made to avoid infestation by dermestid beetles, ants and others.
An excellent add-on, traps can be sold to the account along with extra attractant for re-baiting the traps, or traps can be installed and serviced by the technician. In addition to reducing wasp numbers in individual accounts, large-scale trapping programs have been shown to substantially reduce the number of wasps and consequently the number of stings at outdoor fairs, festivals and sporting events where food or beverages are served. Similar results have been reported for trapping programs on school grounds.
Commercial traps for yellow jackets are available as well as commercial concentrated bait lures. The concentrated lure can be diluted with water when placed in the trap, though best results are obtained when diluting instead with a carbonated beverage such as soda or beer. The bubbles help disperse the scent faster and some think the carbon dioxide filling the trap helps to quickly suffocate the wasps, which will otherwise die in the liquid.
When placing these traps, it is best to use a larger number of smaller traps, rather than a smaller number of large traps. Traps should be checked after 24 hours and their location adjusted based on capture results. Sunny spots near food or garbage often work best.
While late summer and fall are the main season for yellow jackets becoming pests as they forage for carbohydrates, they also can be pests in early summer as well, when they forage primarily for protein. Some commercial lures contain protein; otherwise, traps can be baited with ground beef or tuna (expect to catch a number of flies in such a trap baited with meat as well). It is important to remember, and to tell your accounts, that traps will not attract wasps to an area, but rather provide a level of control with a competitive food source for wasps already in the vicinity.
OTHER SPECIES. While yellow jackets are the most common pests among stinging insects, other wasp species and bees also can be pests at times. Species such as paper wasps, bald-faced hornets, honeybees and carpenter bees become pests typically only when nesting in structures or otherwise near human activity. Control is accomplished through nest elimination.
Honeybees are beneficial insects and their nest should only be removed if deep within the walls of a structure. Carpenter bees damage structures by boring into wood to form nesting galleries. They are not social insects and can only be controlled by treating each individual gallery. Simply painting wood surfaces will help to discourage carpenter bees from boring into them.
Hornets and wasps both build paper nests that are best treated directly with insecticides (and/or foam) at night while wearing protective clothing, including a bee veil. When treating paper wasps, it is imperative to treat all individuals, otherwise survivors may rebuild nests in the same area. With all such nest treatments, the nests should be removed soon after treatment to prevent infestation by other insects or rodents. As with other pests, proofing structures is the best way to prevent bees and wasps from nesting in them.