Just a little diddy on one of the more interesting species I’ve encountered over the years while I finish up a longer piece on the Loess Hills of Missouri. The specimen shown here is a male Trichinorhipis knulli. This quirky little species belongs to the equally quirky little tribe Xenorhipidini (family Buprestidae). Members of this tribe are among the few groups of Buprestidae in which evolution of the male antenna has diverged dramatically from the typical condition (i.e., serrate). In the Xenorhipidini, this condition may be considered very extended flabellate or even lamellate. As I mentioned, only males exhibit this antennal modification – females possess typical serrate antennae. The functional significance of this almost certainly involves detection of female sex pheromones. The surfaces of the flabellae in these species are covered with numerous presumably olfactory sensillae that are lacking on female antennae, and males of a related species (Xenorhipis brendeli) have been observed attracted in large numbers to caged live females. This antennal condition appears to have arisen independently in three other groups of Buprestidae as well, but Xenorhipidini is the only non-monotypic tribe in which males of all member species possess the condition.
Trichinorhipis knulli is restricted to southern California and has been encountered most often in the vicinity of Mountain Springs in Imperial County (just north of the Mexican border), where it breeds in dead branches of jojoba, Simmondsia chinensis. Very few individuals have actually been observed in the field – most existing specimens have been reared from caged, infested branches (as is the case with this specimen, which emerged August 1994 from a dead branch I collected in October 1992 – patience prevails!). At only 3.6 mm in length, it is one of the smallest members of the family, but I think you’ll agree that it is just as impressive under the microscope as any of the larger members of the family. The genus is monotypic (although I hear rumor of an undescribed species from west Texas) and has been placed in its own subtribe (Trichinorphidina) within the Xenorhipidini due to unique characters that distinguish it from the other included genera (Hesperorhipis and Xenorhipis). These include its entire (not abbreviated) elytra and broadly rounded pronotum lacking lateral margins. In Hesperorhipis and Xenorhipis the elytra are abbreviated, and the pronotum is quadrate with distinct lateral margins. The organization of the antennal sensillae also differs between Trichinorhipis and these other genera.
The tribe Xenorhipidini is currently being revised by my colleague and friend, Dr. Charles Bellamy, California Department of Food and Agriculture, Sacramento.