A western yellowjacket (Vespula pensylvanica) handles a piece of hydrogel bait that it carried away from a bait station in an experiment conducted by researchers at the University of California, Riverside. Their findings show that a hydrogel substance could provide an effective substitute for meat in insecticidal baits for yellowjackets. (Image originally published in Choe et al 2018, Journal of Economic Entomology)

By Ed Ricciuti

Yellowjackets dearly love meat, as famed big-cat hunter and conservationist Jim Corbett discovered one morning early in the last century when he watched a tiger return to its kill and blow heavily on the raw, exposed flesh, as if to cool it. It turned out that the meat was crawling with hungry yellowjackets, and the tiger was trying to blow them away so it could reclaim its meal.

Ed Ricciuti

It stands to reason that meat should be potent bait for yellowjacket traps and, in fact, several pesticide-laced meats, ranging from canned chicken to kangaroo, have tested well for that purpose. The problem is that no ready-to-use product is available for everyday baiting of yellowjackets in the United States, according to Dong-Hwan Choe, Ph.D., of the entomology department at the University of California, Riverside. Users must mix their own meat bait, which can be messy and costly, and fresh meat has practical limitations, among them cost, decay, and desiccation.

Choe and his colleges report in a new study published last week in the Journal of Economic Entomology on their development of an experimental synthetic alternative bait that, to paraphrase an old saying, looks like meat, tastes like meat, and, as far as western yellowjackets (Vespula pensylvanica) are concerned, must be meat. So, they feed on it and bring it back to their nest, along with the pesticide it contains.

Existing baits for yellowjackets require the user to mix insecticide with their own meat bait, such as canned chicken, which can be messy. A new study, however, finds that a hydrogel substance provides an adequate tactile resemblance to meat to effectively bait yellowjackets in the same fashion. (Image originally published in Choe et al 2018, Journal of Economic Entomology)

The alternative to meat used in the new research is a concoction of canned chicken juice and the pesticide fipronil in a matrix of hydrogel, a gel made of polymers that readily absorbs large amounts of water and swells as a result. The polymer used is polyacrylamide, a compound used in sewage treatment and as a thickener for materials such as grout. Hydrogel is readily available commercially and, even better, the “hydrogel bait,” as the researchers call it, is inert to biological processes and does not deteriorate like meat. And, unlike meat, just as television ads so often say, there is no mess involved.

Not only does hydrogel bait quickly absorb liquid bait for yellowjackets, but apparently it really does feel like meat to them. Studies show that the wasps prefer coarsely ground bits of meat but virtually ignore meat paste, suggesting that, while they are drawn to meat by smell, they will collect and carry it home only if it feels just right. Evaluation of the hydrogel bait by the UC Riverside team shows that the yellowjackets studied cut up the bait and carry it home, just as they do with meat.

The researchers conducted three 24-hour tests at a Southern California country club picnic area and a public park, where monitoring showed yellowjackets were common. Yellowjackets were monitored with traps set with heptyl butyrate, a fruity smelling compound that attracts yellowjackets. Test baiting in the study areas was done from late August through September, when yellowjackets are active, to ensure that any detected decline in yellowjacket numbers was due to effectiveness of the bait, not a seasonal dropoff.

The decline in yellowjacket foraging activity detected by monitoring traps after the bait test was remarkable, ranging from 74 percent to 96 percent. The catch in some traps that had averaged more than 16 yellowjackets for a day’s collection dropped to less than one after the bait test. Counts of yellowjackets going to and from two nearby nests also dropped significantly and within a week ceased.

It is clear, say the researchers, that the hydrogel bait tested “could be used as an effective matrix for yellowjacket baiting.”

“Finding a non-meat material than can replace the actual meat for the yellowjacket baiting has been a long-lasting question for our research group,” Choe says. “It was important to find something that would mimic the tactile characteristic of the real meat. … It might be possible to make a completely meat-free yellowjacket bait.”

Yellowjacket control is important only because they can cause a hazard to people outdoors in places such as picnic areas or even fishermen who leave their catch accessible to the wasps. And, when their populations boom in areas where food is available from human sources, they may adversely impact local populations of other insects through predation and competition.

Correction: An earlier version of this post described the hydrogel used in the experiment as consisting of “acrylamide.” It has been updated to reflect the correct term, “polyacrylamide.”

Ed Ricciuti is a journalist, author, and naturalist who has been writing for more than a half century. His latest book is called Bears in the Backyard: Big Animals, Sprawling Suburbs, and the New Urban Jungle (Countryman Press, June 2014). His assignments have taken him around the world. He specializes in nature, science, conservation issues, and law enforcement. A former curator at the New York Zoological Society, and now at the Wildlife Conservation Society, he may be the only man ever bitten by a coatimundi on Manhattan’s 57th Street.