Chaetocnema hortensis (Geoffroy, 1785)

Pentinsaari, Mikko, Anderson, Robert, Borowiec, Lech, Bouchard, Patrice, Brunke, Adam, Douglas, Hume, Smith, Andrew B. T. & Hebert, Paul D. N., 2019, DNA barcodes reveal 63 overlooked species of Canadian beetles (Insecta, Coleoptera), ZooKeys 894, pp. 53-150 : 53

Chaetocnema hortensis (Geoffroy, 1785) Figure 41

Distribution.

Native to the Palaearctic region, widespread across the region and common in many parts ( Döberl 2010; Konstantinov et al. 2011). Adventive in the Nearctic region (Ontario, Canada).

Canadian records.

British Columbia: Kelowna, 22-Sep-2014 to 03-Oct-2014 (2 exx, CBG); Revelstoke, 21-Sep-2015 to 02-Oct-2015 (2 exx, CBG). Ontario: Brampton, 19-Sep-2016 to 30-Sep-2016 (2 exx, CBG); Mississauga, 24-May-2016 to 26-May-2016 (1 ex, CBG); Mississauga, 19-Sep-2016 to 30-Sep-2016 (1 ex, CBG). Nova Scotia: Cape Breton Highlands National Park, 23-Jun-2013 to 29-Jun-2013 (1 ex, CBG); Elmwood, 01-Nov-2005 (1 ex, CBG); Kejimkujik National Park, 31-Jul-2009 (1 ex, CBG); Truro, 21-Sep-2015 to 02-Oct-2015 (2 exx, CBG). Labrador: Happy Valley-Goose Bay, 19-Sep-2016 to 30-Sep-2016 (1 ex, CBG). Newfoundland: Terra Nova National Park, 04-Jul-2009 (1 ex, CBG).

Diagnostic information

(based on Konstantinov et al. 2011). Body length (excluding head) 1.8-2.1 mm. Habitus as in Fig. 41A, B . Pronotum and elytra with a bronze or green metallic lustre. Four basal antennomeres yellow, antennomere 2 sometimes partly brown, femora brown, tibiae yellow. Pronotal punctures separated by approximately their own diameter. The two innermost elytral rows of punctures on basal half confused, third through fifth rows confused or regular, sixth row confused. Elytral humeral callus well developed. Aedeagus as in Fig. 41C, D .

Bionomic notes.

Chaetocnema hortensis has a wide range of host plants. It mainly feeds on various grasses ( Poaceae ), including cereal crop species ( Koch 1992; Konstantinov et al. 2011). It has been recorded as a minor pest of wheat and barley in Europe ( Pavlov 1960 ' Vappula 1965). Most of the barcoded Canadian specimens were collected with Malaise traps in suburban environments. A few records are from grassland and forest habitats in Canadian national parks.

Comments.

Chaetocnema hortensis has previously been confused with C. borealis R. White, 1996 in Canada. We found that most Canadian specimens in CNC identified as C. borealis actually represent C. hortensis . The elytral punctation of the two species is similarly irregular basally. In C. borealis , the basal antennomeres are brown rather than pale yellow, and the dorsal surface has a blue rather than bronze or green lustre. The aedeagus is differently shaped in the two species ( Fig. 41D, E ). Based on comparison of the type specimens of C. borealis (deposited in CNC) with the diagnoses and figures in the recent revision of Palaearctic Chaetocnema species ( Konstantinov et al. 2011), C. borealis is very similar to (and possibly synonymous with) the Palaearctic C. sahlbergii (Gyllenhal, 1827). Both species inhabit bogs and other types of wetlands ( Koch 1992; White 1996). Records of C. borealis from agricultural fields and other drier habitats reported e.g., by Majka and LeSage (2010) probably represent C. hortensis .

Figures

Figure 41. Chaetocnema hortensis (Geoffroy) A male habitus, L. Borowiec B female habitus, L. Borowiec C C. hortensis, aedeagus, ventral view D C. hortensis, aedeagus, lateral view E C. borealis R. White, aedeagus, lateral view. Scale bars: 1.0 mm (A, B), 0.5 mm (C-E).