Explanation of Names
Greek tri 'three' + rhabdos 'rod'; probably refers to the three pronotal spots
Numbers
ca. 30 spp. worldwide, of which 24 north of Mexico
(1)Size
adult body 5-12 mm; larva 5-10 mm
Identification
third antennal segment shorter than the fourth (a key characteristic)
elytra yellow with longitudinal dark brown or black stripes in most species; 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; some species are metallic green or blue
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
Range
from so. Canada to Central America; introduced elsewhere (e.g., Australia)
Habitat
weedy fields, brushy areas
Season
adults from May to August; larvae from April to June
Food
hosts include 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) and related plants.
Life Cycle
One generation per year; overwinter as eggs; pupate in the soil.
Remarks
The following text applies to an undetermined species (shown
here) that occurs in coastal southern California:
"Abundant from spring to summer on Isocoma venetus. The adults and larvae are found together feeding on foliage of this plant. Larvae are a dark metallic green, and adults are in life bright yellow with dark metallic green stripes." (Torrey Pines State Reserve, San Diego, California)
See Also
In
Galerucella, Ophraella, and
Pyrrhalta, antennomere 3 is longer than antennomere 4 (shorter in
Trirhabda) -- see
key to Galerucinae
Internet References
live adult image of
T. bacharidis (Bastiaan Drees, Texas A&M U.)
pinned adult images of
T. adela, T. borealis, T. canadensis (Gerald Fauske, ND State U.)
host plant associations of 16 species, biology and distribution info (Z. Swigonova and K.M. Kjer, Chrysomela Newsletter)
detailed description of the genus and the 3 Alabama species (
T. bacharidis, canadensis, virgata) (Dennis Rouse, Auburn U.)
