Candidatus Phytoplasma pyri affects behavior of Cacopsylla pyricola (Hemiptera: Psyllidae)

Authors: CRUZ, MIREYA - Heritage University; Cooper, William - Rodney; Horton, David; BARCENAS, NINA - Heritage University

Submitted to: Journal of Entomological Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/18/2017
Publication Date: 9/7/2018
Citation: Cruz, M., Cooper, W.R., Horton, D.R., Barcenas, N. 2018. Candidatus Phytoplasma pyri affects behavior of Cacopsylla pyricola (Hemiptera: Psyllidae). Journal of Entomological Science. 53(3):361-371. https://doi.org/10.18474/JES17-115.1.
DOI: https://doi.org/10.18474/JES17-115.1

Interpretive Summary: Pear psylla, Cacopsylla pyricola (Förster) (Hemiptera: Psyllidae), is a key pest of pear and is a vector of "Candidatus Phytoplasma pyri", the pathogen associated with pear decline disease. Although commercial pear trees are grafted to Phytoplasma-resistant rootstock, a recent report indicated that many C. pyricola in Washington and Oregon harbor this bacterium. Using fluorescence in situ hybridization, we confirmed that Phytoplasma invades internal tissues of C. pyricola suggesting the pathogen is persistently transmitted. Because many persistently-transmitted plant pathogens alter the flight behavior of their insect vectors, we examined the effects of Phytoplasma infection on dispersal of C. pyricola. Flight behavior was investigated using greenhouse bioassays, which demonstrated that Phytoplasma-infected psylla were less likely than uninfected psylla to emigrate from trees and become captured on yellow traps. Pear psylla occurs as two seasonal morphotypes - summerform and winterform - and the effects of Phytoplasma were observed for both morphotypes. Results provide direction for future study of C. pyricola ecology and interactions between Phytoplasma and psyllid vectors.

Technical Abstract: Pear psylla, Cacopsylla pyricola (Hemiptera: Psyllidae), is a key pest of pear and is a vector of "Candidatus Phytoplasma pyri", the pathogen associated with pear decline disease. Although commercial pear trees are grafted to Phytoplasma-resistant rootstock, a recent report indicated that many C. pyricola in Washington and Oregon harbor this bacterium. Using fluorescence in situ hybridization, we confirmed that Phytoplasma invades internal tissues of C. pyricola suggesting the pathogen is persistently transmitted. Because many persistently-transmitted plant pathogens alter the flight behavior of their insect vectors, we examined the effects of Phytoplasma infection on dispersal of C. pyricola. Flight behavior was first investigated using greenhouse bioassays, which demonstrated that Phytoplasma-infected psylla were less likely than uninfected psylla to emigrate from trees and become captured on yellow traps. This trend was observed for both seasonal morphotypes of this psyllid. The recent report of Phytoplasma-infection of C. pyricola indicated that more winterform psylla collected from pear harbored the bacterium than did summerform. However, rates of infection were not compared between winterforms that emigrated from pear to overwinter on shelter plants versus those that remained in pear. A field survey conducted in November of 2016 did not indicate that Phytoplasma influenced the propensity for winterform psylla to emigrate from pear orchards and colonize apple trees. Although our study does not help explain the previously reported differences between Phytoplasma-infection of seasonal morphotypes, results provide direction for future study of C. pyricola ecology and interactions between Phytoplasma and psyllid vectors.