Biosystematic classification of Colladonus Ball vectors of "Candidatus Phytoplasma pruni" in the Pacific Northwest (Hemiptera: Cicadellidae: Deltocephalinae)

Authors: Cooper, William; Marshall, Adrian; Lewis, Tamera; COOK, RACHEL - University Of British Columbia; Horton, David; PITT, WILLIAM - Washington State University; REYES CORRAL, CESAR - Washington State University; JOCSON, DOWEN - Washington State University; GARDNER, JOEL - Washington State University; ZACK, RICHARD - Washington State University; ACHEAMPONG, SUSANNA - British Columbia Ministry Of Agriculture And Food, Plant And Animal Health Branch; NORTHFIELD, TOBIN - Washington State University

Submitted to: Proceedings of the Entomological Society of Washington
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/10/2025
Publication Date: 10/16/2025
Citation: Cooper, W.R., Marshall, A.T., Lewis, T.M., Cook, R., Horton, D.R., Pitt, W.J., Reyes Corral, C., Jocson, D.M., Gardner, J.D., Zack, R.S., Acheampong, S., Northfield, T. 2025. Biosystematic classification of Colladonus Ball vectors of "Candidatus Phytoplasma pruni" in the Pacific Northwest (Hemiptera: Cicadellidae: Deltocephalinae). Proceedings of the Entomological Society of Washington. 127(2):141-161. https://doi.org/10.4289/0013-8797.127.2.141.
DOI: https://doi.org/10.4289/0013-8797.127.2.141

Interpretive Summary: The leafhopper Colladonus montanus reductus transmits the pathogen that causes cherry X-disease (also called Little Cherry Disease). The last revision of the genus Colladonus published in 1957 acknowledged a need for more research to determine whether Colladonus montanus reductus is a sub-species of Colladonus montanus as currently classified, or a distinct species. Historical reports on X-disease vectors are difficult to interpret because of the unclear classification of the leafhoppers. Researchers at the USDA-ARS in Wapato, WA along with collaborators examined the species boundaries of the Colladonus montanus group. They provide evidence that Colladonus reductus and Colladonus montanus are distinct species, not sub-species as previously reported. This evidence includes differences in morphology, variation in DNA sequences, geographic distribution, and features of the male courtship song. The classification of Colladonus reductus as a distinct species allows for clear communication with researchers and stakeholders about the biology and management of X-disease and the leafhoppers that transmit the X-disease pathogen.

Technical Abstract: A renewed outbreak of X-disease caused by “Candidatus Phytoplasma pruni” has led to substantial economic losses to the stone fruit industry of the Pacific Northwest, especially sweet cherry. Several leafhopper vectors transmit the pathogen, but Colladonus montanus reductus (Van Duzee) (Hemiptera: Auchenorrhyncha: Cicadellidae: Deltocephalinae) is the primary vector responsible for the current outbreak in Washington. Colladonus m. reductus is one of three subspecies of Colladonus montanus (Van Duzee), along with C. m. montanus (Van Duzee) and C. m. mulsus Ball. Historical reports on Colladonus vector biology are difficult to interpret in publications referring to C. montanus without subspecies identification. The last major revision for this genus published in 1957 acknowledged the need for further research to formally assess the specific classification of the C. montanus group. Our goal was to address the C. montanus species boundaries based on morphology, genotypes, and structure of the male vibrational communications. In this report, we support the elevation C. m. reductus as a separate species, C. reductus (Van Duzee), status reinstated. Colladonus reductus differs from C. montanus in morphology of the male pygofer, absence of a yellow wing spot, genotypes of the 16S, CO1, 18S, and 28S barcoding genes, and features of male vibrational communication signals. Biological observations of C. reductus and C. m. montanus are discussed, including geographical distributions and host plant use.