Identification Atlas of the Vespidae (Hymenoptera, Aculeata) of the northeastern Nearctic region
Matthias Buck, Stephen A. Marshall, and David K.B. Cheung
Department of Environmental Biology, University of Guelph, Guelph, Ontario, Canada N1G 2W1
Nomenclatural note. J.M. Carpenter (pers. comm.) kindly pointed out to us that the correct gender ending for this species is dominula. “Dominula” is the diminutive form of the Latin noun domina (= mistress) and therefore indeclinable (the original combination is Vespa dominula Christ).
Species recognition. This recently introduced species, the only species of the nominate subgenus in North America, is easily recognisable by its colouration (see key), the dense punctation of its mesopleuron and the strong ridging of the propodeum (the latter also present in P. perplexus and sometimes P. metricus, both of which have extremely reduced yellow markings). Polistes dominula is very similar to several Palaearctic species from which it can be separated using the key by Dvořák and Roberts (2006).
Variation. Fore wing length 9.5–13.0 mm (♀♀), 8.5–12.0 (♂♂). This species shows relatively little variation. Female clypeal disc with well developed black central spot, with two smaller spots or entirely yellow. Female mandible black, sometimes with yellow spot. Black subantennal mark of female rarely with a pair of small, yellow spots. Female vertex sometimes with a pair of minute yellow spots behind hind ocelli. Yellow postocular stripe usually broadly interrupted near middle, rarely complete but narrowed. In male yellow spots of posteroventral corner of pronotum sometimes confluent with yellow transverse stripe across pronotal carina. In female yellow stripes along pronotal hind margins rarely confluent with stripe of pronotal carina. Female rarely lacking yellow, comma-shaped scutal spots. Yellow spots of metanotum confluent or separate. Mesopleuron in female sometimes, in male usually with small to medium-sized spot below scrobe. Male with ventral surface of mesopleuron yellow, exceptionally black as in female (1 ♂, ON: Sault Ste. Marie, DEBU). Female metapleuron rarely, male metapleuron usually with upper and lower yellow spots (lower spot less frequently present). Yellow discal spots of tergum 1 confluent with apical fascia or separate, always (?) confluent in male. Yellow discal spots of tergum 2 always present, in male sometimes very large and confluent with apical fascia and then often enclosing small black spot. Male with yellow spot at base of sternum 2 very variable, in extreme cases confluent with apical fascia or represented by a swarm of small, evanescent spots. Reddish-orange areas very restricted, limited to flagellum, femora (between black and yellow markings) and inner surface of tibiae. Male with ventral surface of fore coxa always, mid coxa almost always and hind coxa sometimes marked with yellow.
Distribution. Canada: NS (first record 2003), ON (first record 1997) and BC (first record 2003) (Borkent and Cannings 2004, Hoebeke and Wheeler 2005). U.S.: ME to WI, MI, OH and VA, also MO, CO, UT and WA to CA (Arduser and Stevens 1999, Landolt and Antonelli 1999, Cervo et al. 2000, Hoebeke and Wheeler 2005). Palaearctic and Oriental: central and southern Europe to Mongolia and China, south to northern Africa, Israel, Iran, Afghanistan, Pakistan and northern India. Introduced in Western Australia, Chile (Carpenter 1996a) and Argentina (Sackmann et al. 2003). According to K.M. Picket (in litt.) the species is widespread in the U.S. Midwest and is now expanding its range into the southwestern states (AZ, NV). The species was introduced first into Massachusetts in the 1970’s, and was first recorded from Michigan in 1995 (Judd and Carpenter 1996). The first Canadian records from Ontario (Windsor, Guelph, Niagara Falls; see material examined and Hoebeke and Wheeler 2005) indicate that the species was already widespread in southwestern Ontario in 1997. The northernmost records in Ontario are from Pancake Bay Prov. Pk. (2007; collected by K.N. Barber, DEBU), Sault Ste. Marie (2005; collected by K.N. Barber, DEBU), Manitoulin I. (2005; H. Goulet, pers. comm.) and Ottawa (2006; H. Goulet, pers. comm.). The species is still spreading rapidly, should already be present in Quebec, and will soon be found in New Brunswick and Prince Edward Island. According to R. Roughley and T.D. Galloway (in litt., December 2007) the species has not yet been found in Manitoba.
Biology. The introduction and rapid spread of P. dominula in North America has spawned a series of investigations on its biology, especially in comparison with the native North American P. fuscatus, with which it is sympatric throughout the eastern portion of its range. Polistes dominula builds its nests in sheltered places like P. fuscatus but it shows a much greater propensity to use manmade structures (eaves, etc.) (Silagi et al. 2003). This may account for the fact that P. dominula has become much more abundant in urban and suburban areas than P. fuscatus. According to Gamboa et al. (2002) P. dominula has completely replaced P. fuscatus in certain areas of Michigan. This is not the case in Ontario where the two species have coexisted almost as long as in Michigan, even though P. dominula is now much more common in heavily disturbed habitats. Further biological differences between the two species include a much broader prey spectrum (including insects from many other orders besides caterpillars; Cervo et al. 2000), greater tendency to store nectar (Silagi et al. 2003), higher productivity (e.g., due to lesser body mass in P. dominula; Armstrong and Stamp 2003), shorter larval and pupal development times, lesser incidence of parasitism by Strepsiptera (we have not seen any stylopized P. dominula so far), and higher winter mortality (in Rochester, MI) for P. dominula (Gamboa et al. 2004).