Incidence of 'Candidatus Liberibacter asiaticus' in a Florida population of Asian citrus psyllid

Authors: Hall, David

Submitted to: Journal of Applied Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/19/2017
Publication Date: 1/11/2018
Citation: Hall, D.G. 2018. Incidence of 'Candidatus Liberibacter asiaticus' in a Florida population of Asian citrus psyllid. Journal of Applied Entomology. 142:97-103.

Interpretive Summary: An assessment was conducted in Florida of the incidence of Asian citrus psyllids infected by the bacterium responsible for citrus greening disease. This is a serious invasive citrus disease currently jeopardizing citrus production in the USA. Greater percentages of females were usually infected than males, but there were no differences between sexes with respect to pathogen titers. Overall an average of 18% of adults were identified as infected. Incidence of the pathogen in psyllids was frequently pronounced during late fall and early winter and less pronounced during mid to late summer. Transmission rates would be expected to be highest during periods when psyllid infestation levels are large, a high percentage of psyllids are infected, and citrus flush is abundant. This information is important for developing Integrated Pest Management (IPM) programs to manage citrus greening disease.

Technical Abstract: A study was conducted to assess the incidence of a bacterium ‘Candidatus Liberibacter asiaticus’ in a Florida population of Asian citrus psyllid (ACP), Diaphorina citri. The bacterium is the presumed causal agent of Asiatic huanglongbing, a serious citrus disease also known as citrus greening or yellow shoot disease. Adult ACP were periodically collected between May 2010 and September 2012 in a block of diseased trees located near the town of Fort Pierce. The psyllids were subjected to molecular analyses (quantitative polymerase chain reaction assays using HLBaspr primers and a CT cycle threshold of 36) to determine if the bacterium was present and, if so, titer of the pathogen. Significantly greater percentages of females usually tested positive for the pathogen than males, but there were no significant differences between males and females with respect to titers of the pathogen. No significant differences were found among the three ACP color morphs with respect to incidence of the pathogen. Among 47 sample dates, a mean ± SEM of 18 ± 1% of adults per sample date tested positive for the pathogen with a mean cycle threshold (CT) value of 30.2 ± 0.2 among these psyllids. Incidence of the pathogen was generally most pronounced during late fall and early winter (greater than 40% ACP carrying the pathogen) and often least pronounced during mid to late summer (less than 10% carrying the pathogen). Air temperature appeared to be an important factor influencing incidence of the pathogen – there was a significant negative correlation between percentages of ACP testing positive and average daily air temperatures. Transmission rates would be expected to be highest during periods when infestation levels of ACP are large, a high percentage of adults carry a high titer of the pathogen in their salivary glands, and citrus flush is abundant.