New and old weapons in the continuing battle against yellow jackets

Social pests come in all types, including such winged varieties as yellow jackets. While they enjoy their own kind, they are all too eager to leave their gathering and join yours. Called social wasps for their colonizing habit, yellow jackets can be a real summer nuisance around barbecues, pools, picnics, and campsites.

Nuisance wasps of the West are the Western yellow jacket (Vespula pensylvanica), the common yellow jacket (V. vulgaris), and V. germanica-a recent arrival in central California and the Northwest. Predominantly ground nesters, these three scavenge around humans for sustenance. (Similar-looking aerial nesters do not scavenge.)

In parts of the West that had a drier than normal winter, nest building got an early start and wasps could cause you problems sooner than usual.

When weather starts to warm, fertile queens come out of hibernation, choose nest sites (often abandoned rodent burrows), build multicelled nests, and lay an egg in each cell. The first worker wasps to hatch take over the tasks of nest building and feeding the queen's fast-multiplying brood. As workers increase, yellow jackets become greater pests, at their worst from the end of summer into fall. By late fall, nests are abandoned, new queens took for places to overwinter, and the others die.

Wasps need moisture, protein, and sugar. Generally, into August they're after protein, such as your hamburger or the cat's dinner. Once nest building is done, they tend to go more for sugar-overripe fruit, juices, soda pop. They always need moisture from a dripping faucet, bird bath, or swimming pool.

Cautions and precautions

By understanding the wasps' needs, you can try to avoid situations that attract them. Rinse food and drink containers before discarding. Seal garbage cans tightly. Pick up fallen fruit. Use cups with lids and straw holes. Avoid feeding pets outdoors and leaving sweet drinks or meat uncovered. Reduce water sources. Remember, wasps sting when you threaten a nest, swat at them, or accidentally trap one against your skin. Look closely at pool towels or cold drinks. Avoid going barefoot.

Going for the kill

If you know a nest's location, call a professional exterminator. Aerosol sprays that list yellow jackets among target pests work if you score a direct hit; otherwise you have an angered wasp targeting you. While experts strenuously warn amateurs not to spray nests, there is an aerosol product for this use. It shoots a 20-foot stream; directions say to use it only after dark because the wasps depend on the polarity of sunlight to navigate.

If you use traps, place them on your property's perimeter where wasps enter your turf, at least 5 yards downwind of a barbecue or picnic table (wasps hunt into the wind). Traps should be waist high or lower, in moving air but not strong wind, in morning sun and afternoon shade. Put out extra traps I to 2 hours before a party. (Many experts believe traps do not reduce wasp numbers significantly)

Only one in secticide--encapsulated diazinon (Knox Out)-is registered in the West (excluding Alaska and Hawaii) for use in baits to control scavenging yellow jackets. But even when mixed with meat, diazinon is still basically repellent to yellow jackets. It will work, though, when wasps are hungry enough and there is no other food source around.

Synthetic baits such as heptyl butyrate are attractive to V pensylvanica and very slightly to V vulgaris, but not to V. germanica. Best early-season food baits are liverwurst, chicken, ham, fish, and pet food. Later, switch to spoiled fruit, jam, or soft drinks. Don't allow bait to dry out. Besides the traps pictured here, you might consider fly traps (pages 72 and 73 in the July 1987 Sunset). Yellow jackets are attracted to the easy pickings of dead or dying flies; they enter the traps to get the flies and find themselves caught.

Also devised for other purposes, but effective for yellow jackets (and, unfortunately, beneficial insects), is a sticky nontoxic paste (Stikem Special) for trapping the Mediterranean fruit fly. Cost is $5 per pound. For yellow jackets, spread a 1/16-inch layer in a shallow, disposable container; I pound covers 5 square feet. Add about a tablespoon of meat bait. Order the paste from Seabright Ltd., 4026 Harlan St., Emeryville, Calif. 94608.

Look for traps, bait compounds, and sprays at home and garden centers, hardware stores, and nurseries. For a list of publications on safe controls of yellow jackets and other insects, send $1 to BioIntegral Resource Center, Box 7414, Berkeley 94707. Sterling International's customer service line also offers help: (800) 666-6766.