Synonyms and other taxonomic changes
Trirhabda eriodictyonis Fall 1907
Explanation of Names
The epithet refers to the host plant genus Eriodictyon, in the Boraginaceae (formerly Hydrophyllaceae).
Head to posterior tip of elytra: 5-9mm
Body: Overall shape oval; ground color pale-tawny to bright yellow, including ventral side of abdomen.
Elytra: Often slightly darker-yellow than body with a grayish cast due to relatively conspicuous dense, short pubescence. Markings on each elytron vary from nearly absent, to a short dark humeral streak, to (most commonly) a thin, brownish (less commonly greenish-black) longitudinal stripe along the outer lateral edge, and even thinner (to absent) such stripe along the inner sutural edge.
Pronotum: Yellow with shiny luster; pronotal spots small, black, without metallic luster.
Head: Occipital plaga (= medial spot on top of head) black, without metallic luster. Relatively small (narrower than 1/3 distance between eyes), very narrowly linear (in females) to rectangular or "hour-glass" shaped (in males)(1)
. Plaga has relatively constant width...not significantly broadening
to form a wide tongue-like spot covering the rear portion of head.
Legs: Usually entirely pale, bright, or muddy yellow. Black "spot" at joint-like tips of femora, on last two tarsi, and occasionally lightly streaked on tibiae.
, in particular southern CA.
Found in chaparral of mountains and canyons where its host plant Yerba Santa (genus Eriodictyon) grows.
Adults are out from roughly May to August(1)
Larvae and adults feed on species of Eriodictyon
(Boraginaceae). Previously recorded on E. californicum
, E. crassifolium
, and E. angustifolium(2)(1)
, it has also been found on E. trichocalyx
by at least three BugGuide contributors, and E. tomentosum
by another. And a 2014 CSU Northridge Master's Thesis by Katherine Gould
studied host preferences of T. eriodictyonis
between the hairy leaves of E. crassifolium
vs. the sticky leaves of E. trichocalyx
The following quotes are excerpted from Gould(2014)
Eggs hatch from February to March at the base of the host plant. Newly hatched larvae are about 2mm long and climb up the stem of the host plant to leaves, which are their sole food source.
Larvae go through three instars over about 90 days (Hogue 1970), growing to 10 mm in length on average. The first two instars are black, and the third is metallic green. Pupation happens in the soil, where each larva uses bodily secretions to glue together a loose shelter of leaves and soil.
Adults live for about 90 days. Mating occurs on the leaves of the host plant. Females descend to the soil to lay eggs at the base of the host plant, and those 1-mm-long eggs remain in the soil over the winter. The same size and color as grains of sand, these eggs have not been observed in the field.
Mating in T. eriodictyonis is prefaced by no obvious courtship. The male approaches the female and mounts, grasping the edges of her elytra with his tarsi. He strokes her head and pronotum with his antennae while extending his aedeagus. If the female accepts him, she allows him to insert his aedeagus through the notch at the posterior end of her abdomen. Once his aedeagus is inserted, the pair stops moving and remains still for 10 minutes on average before the female starts twisting her body quickly back and forth in what appears to be an attempt to dislodge the male. She will continue this "waggle" behavior until he removes his aedeagus and dismounts, on average 9 more minutes.
If a female chooses not to mate with a male, she will curl up the posterior tip of her abdomen, preventing him from inserting his aedeagus, and waggle her body. Both males and females will mate with multiple partners.
Females lay multiple clutches of eggs over the course of the summer. In the lab, they lay eggs regardless of whether they have mated.
Other than T. eriodictyonis
and T. diducta
, only one other species, T. flavolimbata
from coastal CA, has been reported to have been seen on Eriodictyon
, but that was considered an accidental occurrence and Eriodictyon
is not currently considered a host plant for that species (see "Food" entry on the T. flavolimbata Info page
is the sister species to T. eriodictyonis
and the only other Trirhabda
species having Eriodictyon
as its host plant (all other Trirhabda
species use plants in the Asteraceae). It generally has larger pronotal spots
; a wider occipital plaga
; and significantly wider and darker lateral and sutural stripes on each elytron...as well as a distinct median dark streak between those stripes. The range of T. eriodictyonis
is mostly to the south of that of T. diducta
, with some overlap in CA and UT (cf. pg. 8 of Swigonova & Kjer in "Print References" below).
is typically almost entirely pale yellow and can look quite similar to T. eriodictyonis
. However it's smaller (5-7mm), and the elytal markings are restricted to a short humeral spot or streak. It also has a very different host plant genus (Brickellia
, in the Asteraceae); and its range is Arizona to Texas (i.e. disjunct to the southeast from that of T. eriodictyonis
Gould, Katherine (2014). Host-Specificity and its Effect on Mate Choice in a Plant-Eating Beetle. Master's Thesis, California State University, Northridge. (Full Text
Wilcox, J.A. (1965). A Synopsis of North American Galerucinae (Coleoptera: Chrysomelidae). New York State Museum and Science Service Bulletin No. 400. ((3)
Z. Swigonova & K.M. Kjer, (2001). "Will Molecular Phylogenetics Elucidate Host-Plant Shifts in Trirhabda LeConte (Chrysomelidae,Galerucinae)?", Chrysomela Newsletter No. 40/41, p.3 (PDF here
2014 CSU Northridge Master's Thesis
comparing responses of T. eriodictyonis
to two plant host species: Eriodictyon crassifolium
(with hairy leaves) and E. trichocalyx
(with sticky leaves).