Polistes dominulus; Another Problem

In mid February 2005, Bob Muller of Connecticut wrote me:

"Bill,

This is the problem species. They are not attracted to fish, beer and brown sugar mix or Yellow Jacket traps. They only feed on larvae of butterflies, moths, etc."

Earlier, Bob had written, "Are you aware that the introduced Paper Wasp is killing off EVERY species of moths and butterflies ??

"Polistes dominulus was first found in Massachusetts about 1981 and has spread to the southern states and across the country to the West Coast.

"Some how or some way we all have to get together and kill off this new Paper Wasp species. They don't seem to be found in woodland areas and do colonize in populated areas where they build their hives on or around buildings.

"Not ONE larvae lived more then two days on my trees this past year, I watched these wasps consume every butterfly and moth first instar larva all year.

"Groups of Promethea, Cecropia larva were eaten within hours after hatching. Single larva of Swallowtails, Monarchs, etc were also consumed as well. I spent over five days netting and killing these wasps on my property until they were no longer seen. Once the wasps were gone, exposed larvae on my trees were not touched, and the larvae developed into their normal cocoon stage.

"I sure don't want to push the panic button, but we are heading to the SILENT SPRING for Moths & Butterflies. This was the lowest ever number of Monarchs on record and I feel it was in part caused by this new Wasp.

"We ALL better wake up and see how to stop what's happening."

In an earlier email, Bob had sent me some communication from Whitney Cranshaw of Colorado to David L. Wagner of Connecticut:

"I most definitely think that Polistes dominulus has had an adverse, sometimes dramatically adverse, impact on Lepidoptera in at least some parts of Colorado. I have stated this publically many times and you can definitely put me down as a personal communication reference.

"This was even more strongly developed during incidental conversations over the past two weeks in programs with which I have been involved.

"Last week I did some programs in Utah, then returned for Master Gardener training in Denver. Yesterday and the day before I was doing additional all-day training sessions with Master Gardeners in two other counties. In every spot where I have spoken over the past two weeks, Polistes dominulus and potential impacts on insects has come up - incidentally. The common thread was the great reduction in garden caterpillars (e.g., cabbage "worms", hornworms) and butterflies in the past couple of years.

"This is, of course, only anecdotal. But is closely conforms to what I have seen over the past couple of years - a dramatic reduction in gardn caterpillars. In every garden after around mid-July there are essentially no caterpillars, few butterflies, but there is the ever present cruising of a few P. dominulus adults.

"This species has colonized the Rocky Mountain region extraordinarily quickly. Not known here before 2001, it is essentially now somewhere in every Colorado county and much of Utah. I am not sure about the higher elevation areas, but at least in the lower elevations (e.g., 4000-6000 ft) it appears to be generally established in all areas of human habitation.

"Again, I do not know about the upper elevation areas - I hope to find out more when I lecture there later this month. (I have four more Master Gardener talks in the next couple of weeks in these sites.)

"I also suspect that the incidence of this insect is restricted to areas of suitable nesting habitat. It thrives around human dwellings, which provide nest sites. I think it is largely absent from areas where such nest sites are unavailable.

"My take on this is that this insect is having a huge impact on Lepidoptera near areas where suitable nest sites are present - areas of human dwellings being most prominent.

"I hope this is some help and I regret the delayed response. I am in the office Friday and Monday and will answer any follow-up questions you send me received before then."

This reply from Whitney was in reponse to David's note, partially included below:

"Yellow jackets and paper wasps (Vespidae) are voracious caterpillar predators with seemingly uncanny and nearly always lethal ability to locate Lepidoptera of all instars (Gillapsy 1979, Gould and Jeanne 1984, Preston-Mafham and Preston-Mafham 1988, Montllor and Bernays 1993).

"Two European vespids, Polistes dominulus and Vespula germanica, have become locally abundant in the Northeast and elsewhere across the United States (Gamboa 2002); there is growing concern that these too may be impacting native butterfly and moth species."

In response to Bob's initial messages, hopefully the following will help you idenitfy and eliminate these introduced lepidoteran predators, at least temporarily.

I have not seen this particular species yet on Prince Edward Island, but it may be here. Since their introduction to the United States in the late 1970's or early 1980's, these wasps have been seen in almost all the continuous, continental United States (Maine to Washington and California), at least as far south as Virginia. It is probably everywhere except in Alaska where seasons may be too short and winters too cold.

P. dominulus is slightly smaller than our indigenous yellowjacket and looks very similar. As far as I am concerned, both species should be treated the same way These thin-wasted wasps fly with the hind pair of legs trailing below the abdomen.

The nest is shaped like an upside-down umbrella. The cells are open and can be seen from below. Larvae are cream-coloured and legless and remain within their cells until they emerge as adult wasps.

This particular nest is under the steel girder of a bridge over the west branch of the DuPage River at Winfield, Illinois.

Bruce Marlin image copyright from http://www.cirrusimage.com/

Unless you have the patience and persistence of Bob Muller, who netted his population to oblivion, destroying the nest is probably the quickest and most effective method of eradication.

Fortunately yellowjackets and this new introduction return to their nests at night and become relatively inactive. Approaching in the very late evening or early night with a flashlight is your best chance for success without getting stung.

Hanging nests can be dropped into a large plastic bucket with some gasoline in the bottom. Again work at night. Several years ago I was on a ladder, painting the soffit of the house, and found a yellowjacket nest approximately six inches across.

It was "welded" to the underside of the roof so I used a six inch wide trowel (flashlight in my mouth, bucket in one hand, trowel in the other, knees wedged inside ladder poles) to separate it and drop it into a large plastic bucket. I snapped the lid on tight immediately, quickly descended and shook the bucket.

You might want to work with a smaller knife and a partner. Working at night is important and I wouldn't recommend shorts or a short sleeved shirt. Gloves would also be a good idea and a hat wouldn't hurt either.

It bothered me only slightly to hear the little devils beating their heads against the side of bucket and top. They were still at it the next morning. I don't think I opened the bucket for three days, not until I could shake it and not hear any more flight collisions. Only then did I open the bucket, pour out the gas and nest and burn it.

It might be better to use the bucket without the gasoline to avoid the potential of any dangerous spills, especially on a ladder. Don't open the bucket until all buzzing has stopped. Cook them in the sun for a few days if you like!

I generally do not like killing any of God's creatures, but mosquitoes and blackflies and yellowjackets, and now these invasive wasps, cause me the least concern.

Sometimes yellowjackets make nests underground. Again it is best to work at night, anticipate any direction in which a fire might spread and take precautions and have appropriate fire fighting implements handy.

Find the nest by watching the flight of the wasps, pour gas down the hole (AT NIGHT) and then drop the lit match after you have removed the gas container far from the site. NEVER spray or pour gas on a fire or on coals or embers. Gas treatment always precedes the match.

Fertilized queens from the previous year begin new colonies of P. dominulus each spring. Thus it is important to find the nest and destroy it while all occupants are at home. The life history of these insects is fascinating. The queen deposits small, elongated eggs, one in each cell. The eggs hatch in just a few days, and the queen feeds her young the remains of masticated caterpillars.

The wasp larvae mature and emerge as worker females in as few as forty days.

Good places to look (carefully) for nests include protected locations such as under and within the eaves of structures, in attics and wall voids, and in many other enclosed areas. Some of the more notable locations where nests have been encountered include exterior lighting fixtures, parking meters, animal skulls, bird boxes, and infrequently used equipment like gas grills, motor homes, boats, and autos.

I still recommend watching the wasps to see where they are carrying their prey. Uncover the nest one night if you have to, and then destroy it the next, after you've had a good chance to oberve it in daylight, if need be. Messing with these wasps during daylight hours can be very painful. Fortunately they do not seem to be as aggressive as our indigenous species unless you really disturb them.

From http://www.ento.psu.edu/extension/factsheets/dominulus.htm I have taken the following information:

"Every attempt should be made to limit suitable nest sites. Repair holes in walls, caulk cracks in soffits and eaves, and screen vents and louvers. Nests made early in the season by founding queens are easier to eliminate before workers are produced. During this period it is easy to knock down exposed nests and kill the queen. Nests that have several workers can be treated with a wasp and hornet spray.

" These sprays produce a stream of insecticides that can shoot up to 20 feet from the nozzle. Treatments should be made at night when all the workers and the queen are on the nest. Those nests located within eaves and soffits can be treated by applying an insecticidal dust to the openings of the voids. Blow the dust into the opening, taking care not to breathe dust that becomes airborne. Select a dust that is labeled for this type of application.

"Appropriate dusters available include bulb dusters and plunger or pump dusters. Pest control firms also provide services to control paper wasps.

"Pesticides are poisonous. Read and follow directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams, or ponds.

"*** Disclaimer ***

"Authored by: Steve Jacobs, Sr. Extension Associate, March 2002, Revised October 2003"

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Additional references:

http://iris.biosci.ohio-state.edu/projects/doomproj.html