[Stinging Insects] Hunting Polistes dominulus

Many pest management professionals now have had the opportunity to experience preventive and curative pest management applications for the Polistes dominulus (PD) paper wasp, an invasive structural pest. Since its first discovery in Cambridge, Mass., in 1981, PD had spread west to Minnesota, south to Virginia and is now established on the west coast from Seattle, Wash., to Southern California. Just this summer, Jeff Hahn, an entomology extension specialist from the University of Minnesota, confirmed the first Polistes dominulus specimens from the St. Paul-Minneapolis area.

PD ID. Polistes dominulus appears to be a wasp caught in the middle of a morph. It’s beautiful color pattern is like that of a yellowjacket, juxtaposed against what’s clearly a paper wasp-style nest, can be confusing to an inexperienced pest management professional.

Here are three helpful characters to identify PD:

1. PD has a Polistine (paper wasp) body type, having a tapered first abdominal segment.

2. The yellow and black striped coloration (see photo 1 at right), orange funicle of the antennae (see photo on page 58) and overall smaller body size than most of our native species, provide definitive body characters for the identification of Polistes dominulus.

3. The third way to identify PD is the nest itself. This wasp doesn’t always orient its brood cells at 90 degrees to the ground, but may orient cells from 90 to 180 degrees (see photos 2 and 3 below). This permits a wider variety of potential nest sites because PD exploits voids more often than exposed areas for nest construction (this is a key behavior that assists in management efforts).

The native range of PD is Mediterranean Europe, northern Africa and east to western China. Polistes dominulus’ developmental range then, incorporates a wide variety of habitats with an affinity to hot and semi-arid climactic areas. According to scientific literature, PD is a prevalent species in Mediterranean Europe. The Mediterranean coastal regions are warmer (average July temperature of 73°F) than their Atlantic and Pacific counterparts because of nearly landlocked seas. These warmer temperature preferences have an important role in inspection and treatment of this wasp.

BASIC PD BIOLOGY. Like all social Hymenoptera, PD has a complete (holometabolous) life cycle: egg, larva, pupa and adult. Not to de-emphasize or omit the numbers and time frames assigned to each stage in the development of PD, but it’s really more important to understand the impressive reproduction capacity of this creature. Both laboratory and field studies have shown that Polistes dominulus worker productivity is higher than our indigenous species. Several factors contribute to this biological fact:

1. Queens start nest production very early in the spring, from late April through May.

2. For the Great Lakes regions, PD workers emerge roughly in mid-June. This emergence of workers is nearly one month prior to our native social paper wasp species. After the first workers emerge, nest cells essentially double the following month and again by the end of summer. Therefore, more workers should mean a healthy crop of fall reproductives to initiate colonies the following spring. For pest management professionals, both of these facts have immediate and future control implications (see photo 4 above).

MANAGEMENT STRATEGIES. From personal conversations with representatives from companies across the Midwest, many pest management professionals have expressed frustration at the number of additional service requests they log for this pest. From a business perspective, we all know this means less money. From a service standpoint, I think it means doing a better job at unifying biology together with business and creating a treatment strategy that makes both client and company accountants happy!

Here are five management strategies to think about and apply to your company’s program:

1. Polistes dominulus tends to initiate nests within areas (particularly voids) that tend to warm first in the spring, for example: window and door frames (see photo 5 below left), under roof cap flashings, metal light fixtures (see photo 6 on page 62), roof top air-handling equipment, electrical boxes, open pipe ends of fences (see photo 7 on page 64), sign fixtures and outdoor rodent bait stations.

Note: This spring in late April and early May, I visited several accounts that had one- to three-cell PD nests in two-thirds of all the outside rodent stations (black in color). Does this possibly mean warmer temperature preferences (stations absorbing heat from the sun) or are the rodent stations just a good visual cue (large open entrance hole) for nest building? Either way, this is a sting hazard to field technicians and a confirmation of void area treatment strategies.

2. Inspect and treat nests in voids and protected areas. This means more time for applications and more money for the job. Treating voids and cracks and crevices takes more time than just surface applications alone. Don’t forget parked cars (see photo 8 on page 64), camper trailers, mobile homes, playground equipment, etc. Essentially, this is a "cockroach inspection" outside for wasps.

3. How your company handles the timing of applications is also critical to success. There seems to be two principle treatment strategies for PD: Proactive and reactive type services. Reactive services are those applications sold when the nests are clearly established and worker populations are a problem for the client. This usually occurs mid to late summer. At this time of year, it’s advisable (if nest numbers are high) to simply build into the cost of the service a second and possibly third application. Hey, you’re probably going back anyway, might as well get paid for it! Proactive services take a whole different approach. In early spring when PD nests are in the one- to three-cell phase, or before any workers emerge, there’s an excellent opportunity for treatment. Eliminating the colony founding queens means fewer or no nests the rest of summer. Remember, thoroughness and detail of application is critical for this process to work. You may even have to convince the client who is not "seeing" any problems in April and May that this is the time to treat. That’s where PD biology and your education abilities play their roles. Also, this is a good time to quote the client for a pest exclusion service. The power of pest exclusion is unparalleled.

4. Residual products with a quick knockdown are desired to properly manage Polistes dominulus. Residual insecticides placed in, on and around the nest site (don’t forget the dust formulations) will work in nearly every situation.

5. Educating clients is the most challenging component of any IPM program, so communicate your company’s management expectations up front with clients and fewer service problems will arise.

CONCLUSION. In summary, managing Polistes dominulus requires a balanced blend of biology (knowledge), technology (skills) and education based communication with clients (attitude). Each building, situation and client has many variables and should be treated with a certain amount of flexibility, yet maintain solid IPM principles based on the fundamental biology of the pest. So, go out and make your own luck. Happy PD hunting!

The author is a board certified entomologist with Rose Exterminator, Troy, Mich. He can be reached at gwhite@giemedia.com.