Explanation of Names
Trirhabda LeConte 1865
Greek tri "three" + rhabdos "rod". May refer to the three pronotal spots (like rods in cross-section), or to the three linear stripes on the elytra of some species.
Adult 5-12 mm; larva 5-10 mm
Third antennal segment shorter than the fourth (a key characteristic);
Elytral color varies with species (yellow, green, bluish-purple, blackish), sometimes with a metallic luster. Many species have longitudinal elytral vittae [= stripes];
Pronotum yellow with 3 round or oblong dark spots (1 medial spot and 2 dorsolateral spots);
Head yellow with dark occipital [rear top of head] spot;
Larvae caterpillar-like, but, like other beetles, only have the six thoracic legs and (unlike caterpillars and sawfly larvae) no prolegs
Host plant info often critical for species identification.
NA (so. Canada to Central America); introduced elsewhere (e.g., Australia)
Weedy fields, brushy areas
Adults May-Aug; larvae Apr-Jun
Host plants are in the families Asteraceae and Hydrophyllaceae. Larvae and adults usually feed on leaves and flowers of a single plant species or genus: one group of species feeds on goldenrod (Solidago); another group on wormwood (Artemisia); another on Yerba Santa (Eriodictyon); etc.
One generation per year; overwinter as eggs; pupate in the soil.
Gravid female Trirhabda
will often have remarkably distended abdomens...see comment here
In Galerucella, Ophraella
, and Xanthogaleruca
, antennomere 3 is longer than or equal in length to antennomere 4 (shorter in Trirhabda
Blake D.H. (1931) Revision of the species of beetles of the genus Trirhabda
north of Mexico. Proc. U.S. Nat. Mus. 79(2):1-36 (Full text
Blake D.H. (1951) New species of chrysomelid beetles of the genera Trirhabda
. Journal of the Washington Academy of Sciences, 41:324-328. (Full text
Hogue S.M. (1970) Biosystematics of the genus Trirhabda
LeConte of America north of Mexico (Chrysomelidae: Coleoptera). Ph.D. dissertation, University of Idaho, 212 pp.(4) The most complete reference to date.