title: Asymptomatic spread of huanglongbing and implications for disease control.
abstract: Huanglongbing (HLB) is a bacterial infection of citrus trees transmitted by the Asian citrus psyllid Diaphorina citri. Mitigation of HLB has focused on spraying of insecticides to reduce the psyllid population and removal of trees when they first show symptoms of the disease. These interventions have been only marginally effective, because symptoms of HLB do not appear on leaves for months to years after initial infection. Limited knowledge about disease spread during the asymptomatic phase is exemplified by the heretofore unknown length of time from initial infection of newly developing cluster of young leaves, called flush, by adult psyllids until the flush become infectious. We present experimental evidence showing that young flush become infectious within 15 d after receiving an inoculum of Candidatus Liberibacter asiaticus (bacteria). Using this critical fact, we specify a microsimulation model of asymptomatic disease spread and intensity in a grove of citrus trees. We apply a range of psyllid introduction scenarios to show that entire groves can become infected with up to 12,000 psyllids per tree in less than 1 y, before most of the trees show any symptoms. We also show that intervention strategies that reduce the psyllid population by 75% during the flushing periods can delay infection of a full grove, and thereby reduce the amount of insecticide used throughout a year. This result implies that psyllid surveillance and control, using a variety of recently available technologies, should be used from the initial detection of invasion and throughout the asymptomatic period.
authors.affiliation: Department of Mathematics, University of Florida, Gainesville, FL 32611-8105; joann5@ufl.edu bhsinger@epi.ufl.edu.
authors.forename: Jo Ann
authors.initials: JA
authors.lastname: Lee
authors.affiliation: Division of Plant Industry, Florida Department of Agriculture and Consumer Services, Gainesville, FL 32608-1201;
authors.forename: Susan E
authors.initials: SE
authors.lastname: Halbert
authors.affiliation: Department of Plant Pathology, Citrus Research and Education Center, University of Florida, Lake Alfred, FL 33850-2243;
authors.forename: William O
authors.initials: WO
authors.lastname: Dawson
authors.affiliation: Department of Plant Pathology, Citrus Research and Education Center, University of Florida, Lake Alfred, FL 33850-2243;
authors.forename: Cecile J
authors.initials: CJ
authors.lastname: Robertson
authors.affiliation: Department of Mathematics, University of Florida, Gainesville, FL 32611-8105;
authors.forename: James E
authors.initials: JE
authors.lastname: Keesling
authors.affiliation: Emerging Pathogens Institute, University of Florida, Gainesville, FL 32610-0009 joann5@ufl.edu bhsinger@epi.ufl.edu.
authors.forename: Burton H
authors.initials: BH
authors.lastname: Singer
mesh_terms: D000818:Animals; D001424:Bacterial Infections / Q000382:microbiology / Q000517:prevention & control / Q000635:transmission; D002957:Citrus / Q000382:microbiology*; D003198:Computer Simulation; D006430:Hemiptera / Q000382:microbiology*; D007300:Insect Control / Q000379:methods; D008954:Models, Biological; D010935:Plant Diseases / Q000382:microbiology* / Q000517:prevention & control*; D012230:Rhizobiaceae / Q000472:pathogenicity*; D013997:Time Factors
keywords: asymptomatic huanglongbing; control strategies; latent period; transmission model