Prosapia ignipectus

3.1. Both the Lined and Black Maine Forms Are P. ignipectus,

Which Is Distinct from P. bicincta . Morse believed that his Norridgewock specimens represented a geographically disjunct population of P. bicincta , a judgment apparently based solely on the presence of the lined orange pattern characteristic of P. bicincta . GC dissected genitalia of representative males of southern P. bicincta and black and lined specimens from the Maine populations in question. Male genitalia of the black and lined Maine forms are indistinguishable. Both differ from the genitalia of P. bicincta consistent with the subtle interspecific differences in the apices of the styles illustrated by Hamilton [ 7]. We conclude that both color forms belong to P. ignipectus and, in concurrence with Hamilton [ 7], that P. ignipectus is distinct from P. bicincta . The specific difference is also supported by subtle differences in shape between the species ( P. ignipectus more slender and P. bicincta more robust), by the consistent difference in host plant associations noted above, and by the allopatric distribution of the taxa ( Figure 1 View FIGURE 1 ). DNA bar code analysis, based on sequences of a single mitochondrial gene, indicates that the species are closely related [ 25], probably reflecting recent speciation.

3.2. Populations Monomorphic for the Lined Form Are Uniquely Clustered at the Northeastern Species Margin and Separated from Populations Monomorphic for the Black Form by Less Than 10 km. Table 1 View TABLE 1 reports the color forms encountered in 32 P. ignipectus collections made in 2003, 2004, 2006, and 2012 between the New Hampshire border and Norridgewock. These populations represent the northeasternmost part of the species range. To the immediate south, between Norridgewock and the Atlantic coast, Little Bluestem appears to be absent. In some areas east and northeast of Norridgewock , for example, in parts of the Penobscot River Valley , Little Bluestem is abundant but P. ignipectus is absent. In contrast, P. ignipectus is common on Little Bluestem from Norridgewock north almost to Bingham in the Kennebec River Valley and along some of its tributaries to the west as well as in a portion of the Androscoggin River Valley centering on the city of Rumford. North and west of these populations, occasional Little Bluestem patches without P. ignipectus extend up small river valleys into the Longfellow Mountains. The absence of P. ignipectus on Little Bluestem to the north and east indicates that factors other than host plant distribution limit its range.

Populations monomorphic for the lined form ( Figures 5 View FIGURE 5 (a) and 5(b)) lie in a discrete cluster at the extreme northeastern edge of the species distribution ( Figure 6 View FIGURE 6 ). They encompass an area of about 675 km 2 bounded roughly by the towns of Norridgewock, Bingham, Carrabassett, and New Portland. Less than 10 km to the southwest in New Vineyard they are replaced by populations essentially monomorphic for the black form (with the exception of a single male individual taken in New Vineyard in 2004 that had a partially obscured single orange line across the pronotum) ( Figure 6 View FIGURE 6 and Table 1 View TABLE 1 ). These populations are linked to other monomorphic black populations to the southwest by a monomorphic black population in Wilton. The area in which the collections were taken varies in elevation from about 75 to 250 m and consists of low forest cover, broken by bogs, streams, human habitations, and farmland. There are no significant barriers to P. ignipectus dispersal and the roadside habitats in which P. ignipectus occurs are similar throughout the area. All of the monomorphic lined populations lie in the Kennebec River drainage, but this drainage also includes the monomorphic black populations in New Vineyard and Wilton. Monomorphic black populations to the immediate southwest lie in the Androscoggin River drainage ( Figure 6 View FIGURE 6 ).

3.3. A Geographically Limited Area Near Rumford Has Populations with Mixed Color Forms. Most of the populations along the Androscoggin River and its tributaries are monomorphic for the black color form, but three clustered populations, one in Rumford Center and two in nearby South Rumford on the opposite side of the river, exhibit a mixture of black, lined, and partially lined individuals ( Figure 6 View FIGURE 6 and Table 1 View TABLE 1 ). These populations are 45 kilometers from the nearest monomorphic lined population to the northeast. In each case the lined individuals are phenotypically variable: some fully lined and some partially lined, most of the partially lined specimens with a single line across the pronotum. All populations sampled in Maine to the south and southwest of Center Rumford as well as in adjacent parts of New Hampshire were monomorphic for the black color form ( Figure 1 View FIGURE 1 and VT unpublished observations), consistent with Morse’s observations in Maine almost a century earlier [ 18].

3.4. A Few Populations near the P. bicincta-P. ignipectus Species Boundary Exhibit Mixed Color Forms. The AMNH collection includes one black specimen and one lined specimen (two elytral lines but no pronotal line) of P. ignipectus collected in Tuxedo Park, NY, in 1928. It also includes two lined specimens (one male and one female) collected along with two black specimens (one male and one female) on Staten Island, NY, in 1970. A sweep of Little Bluestem 20 km from Tuxedo Park by VT in August 2014 yielded 42 P. ignipectus specimens, all black. The Staten Island site appears to have been obliterated by residential development. Several other AMNH historical collections from northern New Jersey and Long Island , NY, consist entirely of specimens of the black color form.

In 1993–2000 James Bess collected short series of P. ignipectus specimens, some lined and some black, from Little Bluestem in fens near the Michigan-Indiana border, close to what appears to be the boundary between the P. ignipectus and P. bicincta distributions in the central Midwest (see [ 26] for background on the habitats and insect associations). At Liberty Fen in Jackson Co., MI, Bess collected a lined male and a black male. At Sawmill Fen in LaGrange Co., IN, he collected a lined male and a black female. At Indian Bowl Fen and nearby in Berrien Co., MI, he collected a lined male and a black male. At Brant Road Fen in Oakland Co., MI, he collected a lined male.

3.5. Additional Natural History Observations. Little Bluestem, a grass of nutrient-deficient soils, is an attractive host for spittlebugs, probably because it exhibits associative nitrogen-fixation [ 17]. During our sampling we searched for and found Prosapia ignipectus nymphs living slightly below ground level in Little Bluestem clumps, confirming speculation by Morse [ 18] and Boring [ 19] and a statement by Hamilton [ 16] that the nymphs are root feeders.

Also, while surveying the Little Bluestem associated populations recorded in Table 1 View TABLE 1 , we collected four other spittlebug species, all of the family Aphrophoridae : Philaenus spumarius and Neophilaenus lineatus (both introduced from Eurasia) and the native spittlebugs Lepyronia quadrangularis and Philaenarcys killa . Only L. quadrangularis occurred in sizable numbers at multiple sites. It is clearly associated with Little Bluestem [ 17] but has a much broader host range [ 16]. P. killa , in contrast, is a Little Bluestem specialist [ 17]. In this study it cooccurred with P. ignipectus only in West Bethel, the westernmost Maine site sampled. It cooccurs frequently with P. ignipectus on Little Bluestem in Central New Hampshire (VT observations). P. spumarius occurs primarily on broadleaved herbs [ 16] and was likely associated with herbaceous dicots mingled with Little Bluestem. N. lineatus lives primarily on cool season C3 grasses [ 17] and was likely associated with C3 grass species mingled with Little Bluestem.