Pachybrachis bivittatus (Say, 1824)

Barney, Robert J., LeSage, Laurent & Savard, Karine, 2013, Pachybrachis (Coleoptera, Chrysomelidae, Cryptocephalinae) of Eastern Canada, ZooKeys 332, pp. 95-175 : 113-114

Pachybrachis bivittatus (Say, 1824) Habitus 2 ; Map 2 ; Figures 6a , 7e , 8a , 9a, 9b

Cryptocephalus bivittatus Say, 1824: 440.

Pachybrachys albescens Suffrian, 1858: 404.

Recognition.

Body very large, primarily yellow ( Habitus 2 ); prothorax suffused with rufous; elytral punctation confused, with somewhat apparent rows on disc; elytral color pattern bivittate, with outer vitta rarely entire ( Figure 7e ); pygidium yellow ( Figure 8 a ); male size large: length 3.12 ± 0.16 mm, width 1.64 ± 0.05 mm. These characters allow identification of even singleton females.

Distribution.

Pachybrachis bivittatus is a transcontinental species found across Canada and the United States ( LeSage 1991; Riley et al. 2003). In Ontario, it is most common in the southernmost counties. In Québec, it occurs in the Ottawa Valley and in the St. Lawrence Lowlands. The Saguenay Region is probably its northernmost limit ( Map 2 ).

Material examined.

ONTARIO: Carleton Co., Constance Bay, 26.VI.1995, B. F. & J. L. Carr [1♀, CNC]; Elgin Co., New Sarum, 16.VI.1956, W. J. Brown [5♂ 5♀, CNC]; Essex Co., Amherstburg, 6.VI.1936, G. M. Stirrett [2♀, CNC]; Belle River, 26.V.1946, S. D. Hicks [1♂, CNC]; Kingsville, 23.V.1962, Kelyone & Thorpe [1♀, CNC]; same data, except 19.VI.1954, G. B. Wiggins [1♀, ROM]; Pelee Island, 24-27.VI.1935, R. C. Osburn [1♂ 1♀, OSUC]; same data, except 4.VII.1940, W. J. Brown [2♀, CNC]; Point Pelee, 29.VI.1931, W. J. Brown [4♂ 7♀, CNC]; same data, except 1.VI.1933, G. M. Stirrett [3♂, CNC]; same data, except 29.V.1955, S. D. Hicks [3♂ 4♀, CNC]; same data, except 28.VI.1961, Kelton & Brumpton [2♂ 1♀, CNC]; Haldimand Co., Dunnville, 7.VII.1961, W. & W. Plath [1♂, USNM]; same data, except 7.VIII.1961, W. Plath [1♂, USNM]; Kent Co., Thamesville, 15.VI.1930, G. M. Stirrett [1♀, CNC]; Rondeau Park, 5.VI.1985, J. M. Campbell & A. Davies [1♀, CNC]; Lambton Co., Grand Bend, 17.VI.1956, W. J. Brown [1♂ 4♀, CNC]; Lincoln Co., Beamsville, 19.VII.1939, S. D. Hicks [3♂ 3♀, CNC].

QUÉBEC: Argenteuil Co., Carillon, 24.V.1974, E. J. Kiteley [2♂ 1♀, CNC]; Deux-Montagnes Co., La Trappe, 5.VIII.1932, J. Ouellet [1♂, CEUM]; Île-de-Montréal Co., Montréal, F. Knab [1♂, USNM]; same data, except 31.V.1941 [1♀, CEUM]; same data, except 15.VI.1961, M. Larochelle [1♂, CEUM]; same data, except 3-14.VII.1969, E. J. Kiteley [4♂ 6♀, CNC]; same data, except 17.VI, J. Ouellet [1♀, USNM]; Nicolet Co., Bécancour, 24.VI.1967, J. L. Laliberté [1♂, IDM]; Portneuf Co., Neuville, 9.VII.1939, J. Filteau [1♂ 1♀, CEUM]; Sainte-Catherine, 17.VI.1953, J. C. Aubé [1♂ 7♀, LEM]; same data, except 8.VII.1956 [2♀, LEM]; Québec Co., Sainte-Foy, 17.VI.1933, V. Boulet [1♀, CEUM]; Cap-Rouge, 27.VI.1956, J. L. Laliberté [2♂ 2♀, IDM]; Saguenay Co., Rivière Deschênes, 22.VI.1966, A. Franeslier [1♀, CEUM]; Saint-Jean Co., Cantic, 25.VI.1983, on Salix amygdaloides Andersson, A. Larochelle [1♂ 3♀, CNC]; Saint- Maurice Co., Pointe-du-Lac, 3.VII.1937 [1♀, CEUM]; Vaudreuil Co., Rigaud, 12.VII.1908, J. Ouellet [1♂, CEUM].

Host plants.

Pachybrachis bivittatus is typically associated with willows ( Salix spp., Salicaceae ) ( Fall 1915; Barney 1984; Downie and Arnett 1996; Clark et al. 2004 for literature review). In Canada, MacNay (1958) reported a light infestation of Pachybrachis bivittatus on the foliage of willow along the river banks north of Coaldale, in Alberta. In eastern Canada, LeSage (personal observations) observed it on Bebb’s willow ( Salix bebbiana Sarg.), sand-bar willow ( Salix interior Rowlee), and stalked willow ( Salix petiolaris J.E. Smith). Larochelle (see above) collected it on the peach-leaved willow ( Salix amygdaloides Andersson). The larvae feed in the litter, on willow leaves, but only when they are decayed ( LeSage 1985).

Comments.

With its large size, bivittate elytra, and close association with willows, Pachybrachis bivittatus is one of the easiest species to identify.

Figures

Habitus 2. Dorsal habitus of Pachybrachis bivittatus. Scale bar, 1 mm.

Map 2. The known distribution of Pachybrachis bivittatus in eastern Canada. OR - Ottawa River; SLR - St. Lawrence River; SR - Saguenay River.

Figure 6. Pronotum: a reddish, with close-up of marginal bead, Pachybrachis bivittatus b mottled, Pachybrachis spumarius c with black M-mark, Pachybrachis m-nigrum d almost black, Pachybrachis nigricornis carbonarius.

Figure 7. Elytral punctures and coloration: a in rows in deep striae, Pachybrachis luctuosus b confused in basal half, in rows in apical half, Pachybrachis calcaratus c all confused, Pachybrachis hepaticus d confused and mottled, Pachybrachis spumarius e vittate with marginal vitta interrupted, Pachybrachis bivattatus f black, margined with yellow, Pachybrachis nigriconis carbonarius g entirely black, Pachybrachis luridus.

Figure 8. Pygidium: a largely yellow, Pachybrachis bivittatus b with well-defined yellow spots, Pachybrachis cephalicus c with faint reddish spots, Pachybrachis spumarius d black, Pachybrachis atomarius.

Figure 9. Sexes: a male abdomen, ventral view, Pachybrachis bivittatus b female abdomen, ventral view, Pachybrachis bivittatus.