The quest for a non-vector psyllid: Natural variation in acquisition and transmission of the huanglongbing pathogen ‘<i>Candidatus</i> Liberibacter asiaticus’ by Asian citrus psyllid isofemale lines

<div><p>Genetic variability in insect vectors is valuable to study vector competence determinants and to select non-vector populations that may help reduce the spread of vector-borne pathogens. We collected and tested vector competency of 15 isofemale lines of Asian citrus psyllid, <i>Diaphorina citri</i>, vector of ‘<i>Candidatus</i> Liberibacter asiaticus’ (<i>C</i>Las). <i>C</i>Las is associated with huanglongbing (citrus greening), the most serious citrus disease worldwide. <i>D</i>. <i>citri</i> adults were collected from orange jasmine (<i>Murraya paniculata</i>) hedges in Florida, and individual pairs (females and males) were caged on healthy <i>Murraya</i> plants for egg laying. The progeny from each pair that tested <i>C</i>Las-negative by qPCR were maintained on <i>Murraya</i> plants and considered an isofemale line. Six acquisition tests on <i>D</i>. <i>citri</i> adults that were reared as nymphs on <i>C</i>Las-infected citrus, from various generations of each line, were conducted to assess their acquisition rates (percentage of qPCR-positive adults). Three lines with mean acquisition rates of 28 to 32%, were classified as ‘good’ acquirers and three other lines were classified as ‘poor’ acquirers, with only 5 to 8% acquisition rates. All lines were further tested for their ability to inoculate <i>C</i>Las by confining <i>C</i>Las-exposed psyllids for one week onto healthy citrus leaves (6–10 adults/leaf/week), and testing the leaves for <i>C</i>Las by qPCR. Mean inoculation rates were 19 to 28% for the three good acquirer lines and 0 to 3% for the three poor acquirer lines. Statistical analyses indicated positive correlations between <i>C</i>Las acquisition and inoculation rates, as well as between <i>C</i>Las titer in the psyllids and <i>C</i>Las acquisition or inoculation rates. Phenotypic and molecular characterization of one of the good and one of the poor acquirer lines revealed differences between them in color morphs and hemocyanin expression, but not the composition of bacterial endosymbionts. Understanding the genetic architecture of <i>C</i>Las transmission will enable the development of new tools for combating this devastating citrus disease.</p>