Every few years, a persistent rumor circulates, especially in northeastern Washington, that DNR is intentionally releasing yellow jackets as biological control agents to kill forest pests. So, let’s set the record straight: DNR does not release yellow jackets or similar insects.
Many years ago, an entomologist with DNR went on the radio to tell people in Colville, “DNR does not release yellow jackets. No one releases yellow jackets.” But the rumor is back and DNR’s Northeast Region Office is receiving calls from the public about it.
The last time that forest pest control insects 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 http://www.fs.fed.us/outernet/r6/nr/fid/fidls/fidl-96.pdf), a tiny caterpillar that defoliates western larch trees. The tiny wasps that prey on the casebearers are quite a bit 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 any yellow jackets or similar insects since then.
Why so many yellow jackets this year
This year seems to be a banner year for yellow jackets, bald faced hornets, and similar stinging insects. It may be related to the cool, spring conditions that boosted the population of aphids, a popular food source for yellow jackets. Aphids are the full meal deal. They are “meat” to predatory yellow jackets. When aphids suck plant juices, they take in sugary fluids, but not much protein. They keep sucking to obtain more protein, excreting extra, unneeded sugary fluids as droplets that are commonly called “honeydew.” Yellow jackets collect the honeydew droplets from the rear ends of the aphids themselves. Some collect the sticky, sugary liquid or dried sugars from other surfaces like stems, leaves, or parked cars beneath aphid-infested trees. It may have been the honeydew droplets in the spring that are allowing yellow jackets to thrive now.
WSU Cooperative Extension has a bulletin about recognizing and reducing problems associated with yellow jackets: http://cru.cahe.wsu.edu/CEPublications/eb0643/eb0643.pdf
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