Explanation of Names
TRIRHABDA: from the multiple-origin "tri" (three) + the Greek "rhabdos" (rod); probably refers to the three "rod-like" spots on the pronotum of most species
Numbers
27 species listed at
nearctica.com
34 species worldwide (the genus is native to Central America, Mexico, and North America)
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 look like caterpillars, but, like other beetles, only have the six true legs at the front of the body- and none of the
prolegs typical of caterpillars and sawfly larvae.
Knowing the identity of the hostplant can be very important for identifying the species.
Range
throughout United States and southern Canada
also occurs in Mexico and Central America, and has been introduced elsewhere (e.g. Australia)
Habitat
weedy fields, brushy areas
Season
adults from May to August
larvae from April to June
Food
larvae and adults characteristically feed on leaves and flowers of a single species or genus of plant; one group of Trirhabda species feeds on goldenrod (Solidago spp.), and another group feeds on wormwood (Artemisia spp.) and related plants.
They feed on plants of the families Asteraceae and Hydrophyllaceae
1.
Life Cycle
One generation per year; overwinters as an egg; pupation occurs 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 species of
Galerucella, Ophraella, and
Pyrrhalta, the third antennal segment is longer than the fourth (not shorter, as in
Trirhabda) - see
key to Galerucinae at Auburn University
Internet References
live adult image of
T. bacharidis (Bastiaan Drees, Texas A&M U.)
pinned adult images of
T. adela, borealis, canadensis (Gerald Fauske, North Dakota State U.)
live and pinned adult images of
T. adela, canadensis, and possibly
virgata (Insects of Cedar Creek, Minnesota)
distribution and pinned adult images of
T. convergens and
virgata (Harvard U., Massachusetts)
host plant associations; PDF doc of 16 species, plus info on biology and distribution (Z. Swigonova and K.M. Kjer, Chrysomela Newsletter, Coleopterists Society)
detailed text description of the genus and 3 species collected in Alabama:
T. bacharidis, canadensis, virgata (Dennis Rouse, Auburn U.)
distribution in Canada; PDF doc showing list of provinces for 10 species (L. LeSage, Chrysomelidae; Checklist of Beetles of Canada and Alaska)
