DNA barcoding of federally threatened valley elderberry longhorn beetle

For more information contact Andrea Schreier: amdrauch@ucdavis.edu

Background and Significance of Study

The valley elderberry longhorn beetle (VELB; Desmocerus californicus dimorphis) is a federally threatened beetle subspecies endemic to California’s Central Valley. Its unlisted sister taxa, California elderberry longhorn beetle (CELB; Desmocerus californicus californicus), lives at higher elevation in the coastal mountain ranges and Sierra Nevadas. VELB and CELB require elderberry bushes to complete their life cycle. Adult beetles lay eggs on elderberry bushes and after hatching, larvae burrow into elderberry stems. Within the stem, larvae grow and develop for 1-2 years before excavating a conspicuous exit hole in the last stage of development. Adult beetles emerge from the exit holes in springtime, spending the remaining few months of their lives feeding on elderberry leaves, mating, and laying eggs.

Valley_elderberry_longhorn_beetle_FWS

Female VELB (photo by USFWS)

Adult VELB are rarely encountered and therefore the subspecies’ status is very difficult to determine from field surveys. Current survey protocols involve counting new exit holes (those containing frass, or beetle poop) on elderberry bushes. However, it is sometimes difficult to distinguish new exit holes from those made the previous year. It’s also impossible to determine whether an exit hole was made by a VELB or CELB, especially in southeastern areas of the VELB range where the two subspecies’ distributions overlap. Even when adult beetles are encountered, morphological similarities between the subspecies in areas of potential range overlap can confound positive subspecies identification.

We are working with Marcel Holyoak, a VELB expert, to develop genetic and statistical methods to improve VELB survey protocols. Our role is to develop one or more DNA barcodes that can determine whether beetle frass collected from exit holes originated from VELB or CELB. More accurate identification of VELB exit holes will reduce surveying errors and will refine our knowledge of VELB and CELB ranges. In particular, we are interested in better defining areas of potential range overlap between the subspecies.

To develop these diagnostic markers, we are relying on the few VELB and CELB museum specimens that have been collected in the past few decades. So far we have received specimens of both subspecies generously loaned to us by the UC Riverside Entomology Research Museum and UC Davis Bohart Museum of Entomology. We have validated a protocol for non-invasive DNA extraction from these valuable specimens and are currently identifying candidate loci that may be used as barcodes to distinguish between the subspecies.

Desmocerus specimens from UC Riverside

VELB and CELB specimens on loan from the UC Riverside Research Museum of Entomology (photo by Alisha Goodbla)

Project Personnel: Alisha Goodbla, Melinda Baerwald, and Andrea Schreier

Collaborators

Marcel Holyoak, Department of Environmental Science and Policy, UC Davis

US Fish and Wildlife Service