Pterourus bjorkae Pavulaan, 2024

Pavulaan, Harry, 2024, Determination of a new spring-flying species of the Pterourus glaucus complex (Papilionidae) in southern New England, The Taxonomic Report of the International Lepidoptera Survey 12 (1), pp. 1-26 : 14-18

Pterourus bjorkae Pavulaan, 2024

New England Tiger Swallowtail

(new species)

ZooBank registration: urn:lsid:zoobank.org:act:5524CE5E-2146-4F91-A9AD-2E8EC1FE5BD7

Holotype and TL: A female holotype has been designated to represent this species ( Figs. 22-23 ). This is due to the problem of differentiating males from other species within the glaucus species complex. Females are most distinct. The type locality is Great Swamp Management Area , West Kingston , Washington County, Rhode Island, May 15, 1990. An allotype male ( Figs. 24- 25 ) has been designated: Great Swamp Management Area , West Kingston , Washington County , Rhode Island, June 3, 1984. 12 male and 7 female paratypes are retained by the author. Many other paratypes in the collection of the late Alex Grkovich.

Status: Originally viewed as a possible distinct species during my 1983-1984 Rhode Island field surveys. Uncommon resident, though very widespread in occurrence. Generally, only observed as single individuals, less frequently only in very small numbers in Massachusetts. No population irruptions were ever observed or reported.

In many respects, P. bjorkae appears analogous to Appalachian P. appalachiensis , and has been referred to as P. “near- appalachiensis ” by local butterfly observers for several years as of this writing. Intermediate characters between glaucus and canadensis lends to a hybrid origin for appalachiensis through introgression of characters during the last glacial maxima (Kunte, et al, 2011; Ording, 2008; Ording et al., 2009; Scriber & Ording, 2005). This very likely has occurred as well with bjorkae . It is possible that there is still hybridization occurring between this species and siblings glaucus and canadensis . However, this taxon does appear to be a stable, breeding population in southern New England. It also appears to replace canadensis in the southern New England springtime niche, though some canadensis -like individuals have been taken as far south as Rhode Island. On Long Island, N.Y., south of the Long Island Sound, I have taken many bjorkae specimens during the spring months, along with typical glaucus , but canadensis- like individuals are absent.

One consideration was to propose this as a new subspecies of canadensis . However, the presence of small, potential canadensis -like adults sympatric with the larger bjorkae in places like western Massachusetts, northern Connecticut and even Rhode Island, tentatively lends to species status. Much work remains to be done, to determine any relationship with canadensis populations to the north, to determine if they are allopatric (possibly with a hybrid zone), sympatric, or if bjorkae is a southern expression (subspecies) of canadensis .

Habitat: Primarily a resident of deciduous forest habitats, though adults are frequently found in urban and suburban habitats.

Larval Hosts: Black Cherry ( Prunus serotina ) is currently the only confirmed hostplant in southern New England. Prunus virginiana (Choke Cherry) is reported for the “Mid-Summer Tiger Swallowtail” in southern Ontario ( Wang, 2017). Certainly, other hosts are used but require documentation based on rearing. It is not presently known if the larvae can eat canadensis -specific hosts such as Betula spp. (Birch) and Populus tremuloides (Quaking Aspen) , or glaucus -specific hosts such as Liriodendron tulipifera (Tulip Tree) .

Habits: This butterfly appears to be primarily a forest canopy dweller, much as is P. appalachiensis of the Appalachian Mountain region. Adults are mainly observed in rapid flight in forested habitat, coming down to nectar at numerous nectar sources such as Syringa vulgaris (Common Lilac) in the spring, and Asclepias syriaca (Common Milkweed) in late June. The species is not common, and generally only seen as single individuals near the southern coastal region, though they have occasionally been observed in small “puddle parties” in Massachusetts.

Broods: Apparently one brood. Obligate univoltine, corroborated by Hagen & Lederhouse (1985) for New York. Appearance of similar individuals in late summer confuses matters and requires extensive rearing to determine if hybridism influences voltinism. Confirmed early dates: April 30 (Connecticut); May 15 (Massachusetts); May 8 (Rhode Island). Confirmed late dates: June 12 (Connecticut); July 8 (Massachusetts); June 12 (Rhode Island). An overlap of flights with the “Mid-Summer Tiger Swallowtail” has not been documented in southern New England.

Distinguishing features and variation: The largest of the three spring-flying Tiger Swallowtails. Wingspan of measured specimens (N=19) is 75.2-92.1 mm (averaging 84.7 mm), with a forewing length of 43.0-55.3 mm (averaging 49.2 mm). Specimens of bjorkae in this study measured larger than Vermont canadensis . The females of bjorkae are most distinct [thus selection of a female specimen to serve as the holotype] ( Figs. 22 , 23 , 26 , 27 , 34 ). Dorsally, the female individuals are readily differentiated from glaucus by the greatly reduced row of blue submarginal chevrons on the dorsal hindwing, never forming into a solid blue band. Examined specimens and photo images reveals fewer blue chevrons than in canadensis females. Some females nearly lack the submarginal blue chevrons, except always appearing in cells CuA2 and CuA1. This gives some females the appearance of the male phenotype. The interior of the dorsal hindwing is clear yellow and is never covered by the subtle blue wash of scales found in most glaucus females. Also, the female black form has not been documented.

Ventrally, the diagnostic submarginal yellow band on the forewing of bjorkae specimens is solid though the anterior portion of the band may be broken in many individuals. The hindwing is narrower and more angular than glaucus , being somewhat more similar to canadensis and appalachiensis , and is characterized by outer wing edge being more “stair-stepped” and not scalloped as in glaucus . Similarly, the postmedian boundary between interior yellow ground color and the submarginal row of blue chevrons forms a straight black ribbon. The hindwing marginal lunules are shaped more like a row of slanted rectangles, though the shape is variable. In some individuals these marginal lunules may have the look of crescents as in glaucus . Also, the black band along the inner (anal) margin is wide as in canadensis .

The dorsum of bjorkae males ( Fig. 24 ) is intermediate between glaucus and canadensis males and also very similar to males of the other New England “Tiger Swallowtail” species, and can easily be misidentified. P. bjorkae males differ from P. appalachiensis and canadensis by having more rounded wings and a broader black area on the outer portion of the dorsal hindwing; whereas the females differ by having reduced dorsal blue hindwing chevrons and a broader black outer portion of the hindwings. Some females appear male-like. P. bjorkae is also larger than canadensis .

Wang (2017) illustrates a first instar “hybrid” larva from southern Ontario that is intermediate between first instar larvae of glaucus and canadensis , in which the white saddle mark of both (parent) species is present but the posterior and anterior bands typical of canadensis first instar larvae are reduced. Future studies would help document that this is consistent for bjorkae in New England.

Comments: In 1984-1985 and 2006-2007 rearing experiments, females tentatively identified as bjorkae were confined on Prunus serotina , on which they readily oviposited. Approximately 10 ovae were deposited on leaves during each of the two years. The resultant larvae were reared indoors under lab conditions. The larvae produced hibernal-diapausing pupae. In the 2006-2007 experiment, one resultant female ( Figs. 26-27 ) emerged that clearly appears to be intermediate between bjorkae and glaucus , except that she has a near absence of the dorsal hindwing blue chevrons, more typical of bjorkae .

Distributional County Records: Confirmed photo or specimen records for this study. Connecticut: Fairfield, Hartford, Litchfield, Middlesex, New Haven, New London, Tolland, Windham. Massachusetts: Bristol, Essex, Hampden, Hampshire, Middlesex, Nantucket. Norfolk, Plymouth, Worcester. Rhode Island: Kent, Providence, Washington.

Etymology: This butterfly is named in honor of Icelandic singer, songwriter, composer, record producer, music and fashion collaborator, actress, disk jockey, environmental activist, and personal inspiration, Björk Guðmundsdóttir ( Fig. 28 ).

Figures

Fig. 22. Holotype, female, P. bjorkae. May 15, 1990. Great Swamp Management Area, West Kingston, Washington Co., R.I. Leg. Harry Pavulaan. Dorsal view.

Fig. 23. Holotype, female, P. bjorkae. Same data as Fig. 22. Ventral view.

Fig. 24. Allotype, male, P. bjorkae. June 3, 1984. Great Swamp Management Area, West Kingston, Washington Co., R.I. Leg. Harry Pavulaan. Dorsal view.

Fig. 25. Allotype, male, P. bjorkae. Same data as Fig. 24. Ventral view.

Fig. 26. Paratype, female, P. bjorkae. Ex- ova from female of May 1996. West Kingston, Washington Co., R.I. Em: Feb. 19, 1997 (in lab). Leg. Harry Pavulaan. Dorsal view.

Fig. 27. Paratype, female, P. bjorkae. Same data as Fig. 26. Ventral view.

Fig. 34. Holotype (female), Pterourus bjorkae. May 15, 1990, West Kingston, Washington Co., R.I. Dorsal (left), ventral (right).

Fig. 28. Björk Guðmundsdóttir (1995) Photo courtesy Eric Mulet.