Seasonal Patterns in the Frequency of ICandidatus/I Liberibacter Asiaticus in Populations of IDiaphorina citri/I in Florida

Candidatus Liberibacter asiaticus (CLas) is a putative causal agent of Huanglongbing, a serious citrus pathogen. Diaphorina citri Kuwayama (Hemiptera: Psyllidae) is the primary vector of CLas. Florida only has CLas, and the only vector of CLas in Florida is D. citri. We explored patterns in the proportion of psyllids carrying CLas by analyzing psyllids collected from seven field sites from 2008 through February 2012. There was an upsurge in prevalence in the fall and, in some groves, a second peak in the spring. We also found that females were more common in the first and last months of the year. D. citri has different abdominal colors that we grouped into blue/green and gray/brown. Gray/brown psyllids had a higher CLas prevalence than blue/green individuals. We suggest several explanations for these patterns, but the two most likely involve a hypothesized CLas gradient in the first few millimeters of new growth and differences in immune response related to sex and color. In application, the results confirm that psyllid management is always necessary because psyllids carry CLas year-round. The seven study sites had seven levels of management, from abandoned to intensively managed. In general, more aggressively managed groves had fewer psyllids with CLas. A well-managed organic grove was an exception, having low CLas prevalence but abundant psyllids. It is possible that the low CLas prevalence at this grove was due to management techniques or that this area was infected more recently. Candidatus Liberibacter asiaticus (CLas) is one of the putative causal agents of huanglongbing, which is a serious disease in citrus production. The pathogen is transmitted by Diaphorina citri Kuwayama (Hemiptera: Psyllidae). As an observational study, six groves in central Florida and one grove at the southern tip of Florida were sampled monthly from January 2008 through February 2012 (50 months). The collected psyllids were sorted by sex and abdominal color. Disease prevalence in adults peaked in November, with a minor peak in February. Gray/brown females had the highest prevalence, and blue/green individuals of either sex had the lowest prevalence. CLas prevalence in blue/green females was highly correlated with the prevalence in other sexes and colors. Thus, the underlying causes for seasonal fluctuations in prevalence operated in a similar fashion for all psyllids. The pattern was caused by larger nymphs displacing smaller ones from the optimal feeding sites and immunolog