Forest Health Program Manager
DNR, Resource Protection Division
DNR Communications Manager
For the record: DNR does not release yellow jackets. But every few years a persistent rumor circulates, especially in northeastern Washington, that DNR has intentionally released yellow jackets as biological control agents to kill forest pests. People call to complain about the supposed practice, with some people stating that their children have been stung and it’s DNR’s fault. We do our best to squash the rumor when folks call, and once even had one of DNR’s entomologists go on the radio in Colville to tell people that not only does DNR not release yellow jackets, but “…no one releases yellow jackets.” However, when yellow jackets again became plentiful as they did this year, DNR’s Northeast Region Office once again received calls.
Part of the confusion may be that there are some beneficial wasps that provide important control of forest insects:
- Digger wasps locate a soil insect larva, tunnel down to anesthetize it, and lay an egg atop the prey to be a future feast.
- Potter wasps construct a clay chamber and lay one egg inside, provisioning the cell with an anesthetized caterpillar for the wasp larva to eat when it hatches.
- Ichneumonid wasps insert their eggs directly into the bodies of insect larvae, sometimes poking long ovipositors through the bark and outer wood of tree trunks to reach bark beetles and other wood boring insects.
- Trichogramma wasps are egg parasites, inserting their own tiny eggs directly into the eggs of other insects.
- The Douglas-fir tussock moth is parasitized and preyed on by more than 50 types of wasps and flies.
However, the last time that forest pest control wasps were intentionally released in eastern Washington was in the 1960s. Tiny parasitic wasps (Agathis pumila and Chrysocharis laricinellae) were released to combat a non-native insect, the “larch casebearer” (Coleophora laricella), a small caterpillar that defoliates western larch trees. Larch casebearers are so small they reside inside individual larch needles. The tiny wasps that prey on the casebearer caterpillars are much smaller than fruit flies and do not sting humans. That release some 50 years ago proved successful as larch trees are now much less vulnerable to casebearer caterpillar outbreaks. But we haven’t released similar insects since then and we’ve never released yellow jackets.
Why so many yellow jackets this year?
This seems to have been a banner year for yellow jackets, bald faced hornets, and similar stinging insects. It may have been related to the moderately cool spring weather conditions that boosted populations of aphids, a popular food source for yellow jackets and their ilk. Aphids are the full meal deal for yellow jackets: protein and fat when chewed up and eaten as “meat” but also “energy drink” or “dessert” when accessed for sugar. As aphids suck plant juices, they take in large volumes of sugary fluids, but not much protein. They keep sucking to obtain more protein, excreting extra, unneeded sugary fluid as droplets that are commonly called “honeydew.” Yellow jackets may collect the honeydew droplets from the aphids themselves or from the surfaces of stems, leaves, and parked cars in aphid-infested areas. It may have been the abundance of aphids and their honeydew droplets in the spring that allowed yellow jackets to thrive.
WSU Cooperative Extension has a bulletin that may help with recognizing and reducing problems associated with yellow jackets and paper wasps.