Explanation of Names
Disonycha pensylvanica (Illiger 1807)
The three species of the D. pensylvanica-group are hard to tell apart; in some cases examining male genitalia is the only way.
Common features: Head completely, or for the most part, black; pronotum reddish, usually with central dark spot (+ lateral spots casually); elytra always with pure black & white stripe pattern, black stripes wider than white ones.
Characters that work in most cases:
head, legs, antennae always black, also underside, except last ventrite (tergites red, however!);
elytra indistinctly punctured, clearly costate in females;
elytral sutural and sublateral black stripes united at tip;
pronotum with one central macula, which may become enlarged to cover most of pronotum;
5-6.5 mm body length.
Where this combination is not complete, especially, if elytral sutural and sublateral black stripes usually shortly interrupted at tip by reddish color, then:
head usually red around antennal sockets;
legs may have red femora;
all ventrites margined red;
elytra clearly punctured, not costate in females;
pronotum with a central macula and two smaller lateral spots (may fuse, but not disappear);
5.8-8 mm body length.
head usually red anterior of antennal base;
legs usually with red femora, also tibiae can be partly red; (variants with legs all dark occur)
abdomen usually completely red;
elytra finely punctured, +/- costate in females;
pronotum with 0-5 spots (may fuse);
5.6-6.8 mm body length.
e. NA (TX-FL-QC-SD) to C. America [map
usually near aquatic habitats(1)
Normal hosts are Polygonum
spp. including smartweed (Polygonaceae)(4)(5)