“Candidatus Liberibacter solanacearum” (Lso) is an economically important pathogen of solanaceous crops and the putative causal agent of zebra chip disease of potato (Solanum tuberosum L.). This pathogen is transmitted to solanaceous species by the potato psyllid, Bactericera cockerelli (Šulc), but many aspects of the acquisition and transmission processes have yet to be elucidated. The present study was conducted to assess the interacting effects of acquisition access period, incubation period, and host plant on Lso titer in psyllids, the movement of Lso from the alimentary canal to the salivary glands of the insect, and the ability of psyllids to transmit Lso to non-infected host plants. Following initial pathogen acquisition, the probability of Lso presence in the alimentary canal remained constant from 0 to 3 weeks, but the probability of Lso being present in the salivary glands increased with increasing incubation period. Lso copy numbers in psyllids peaked two weeks after the initial pathogen acquisition and psyllids were capable of transmitting Lso to non-infected host plants only after a two-week incubation period. Psyllid infectivity was associated with colonization of insect salivary glands by Lso and with Lso copy numbers >10,000 per psyllid. Results of our study indicate that Lso requires a two-week latent period in potato psyllids and suggest that acquisition and transmission of Lso by psyllids follows a pattern consistent with a propagative, circulative, and persistent mode of transmission.

The potato psyllid, Bactericera cockerelli (Sulc) (Hemiptera: Triozidae) is a serious pest of potato and other solanaceous crops. B. cockerelli has been associated with the bacterium "Candidatus Liberibacter solanacearum" (Lso), the causal agent of zebra chip, a new and economically important disease of potato in the United States, Mexico, Central America, and New Zealand. The biology of liberibacter transmission to potato and other host plants by the potato psyllid is largely unknown. The current study determined Lso acquisition by adult psyllids following different acquisition access periods (AAP) on potato and tomato, quantified Lso titer over time in postacquisition psyllids, determined Lso-acquisition rate in psyllids at each AAP on each source of inoculum, and determined influence of host plant Lso titer on Lso acquisition rates and postacquisition titer in psyllids over time. Results showed that Lso detection rates and titer increased over time in psyllids following AAPs of 8, 24, and 72 h on tomato and potato and Lso titer was highest when psyllids acquired Lso from tomato versus potato. Lso titer ranged from 200- to 400-fold higher in tomato leaves, petioles, and stems than those of potato. The increase of Lso titer in the insects reached a plateau after an average of 15 d following 24 and 72 h AAP on potato or tomato. At this 15-d plateau, Lso titer in postacquisition psyllids was comparable with that of infective psyllids from the Lso-infected laboratory colony. Lso-acquisition rate in psyllids fed on potato and tomato increased up to 5 and 20, 15 and 35, 35 and 75, and 80 and 100%, respectively, when the insects were allowed access to plants for 4, 8, 24, and 72 h, respectively.

The potato psyllid, Bactericera cockerelli (Sulc) (Hemiptera: Triozidae), and its associated pathogen "Candidatus Liberibacter solanacearum" (Ca. L. solanacearum), the putative causal agent of zebra chip (ZC) disease in potatoes (Solanum tuberosum L.), were sampled in commercial potato fields and untreated control plots for 3 yr in multiple locations in Texas, Kansas, Nebraska, and Colorado. Populations of the potato psyllid varied across years and across potato growing regions. However, the percentage of potato psyllids infected with Ca. L. solanacearum although variable across years, was consistently highest in the Lower Rio Grande Valley of Texas (LRGV), the reported overwintering location for this pest. The numbers of Ca. L. solanacearum-infected psyllids collected on field traps and large nymphs counted on leaf samples were both positively correlated with the final percentage of ZC in tubers. In the LRGV, where vector and disease pressure is the highest, population levels of immature life stages of the psyllid and percentage of ZC differed greatly between commercial and untreated fields. These results show that the pest management program that was used can be effective at controlling development of the psyllid and ultimately reducing the incidence of ZC.

The potato psyllid, Bactericera cockerelli (Sulc) (Hemiptera: Triozidae), is a pest of potato and other solanaceous crops in North and Central America and New Zealand. Previous genotyping studies have demonstrated the presence of three different haplotypes of B. cockerelli in the United States corresponding to three geographical regions: Central, Western, and Northwestern. These studies utilized psyllids collected in the western and central United States between 1998 and 2011. In an effort to further genotype potato psyllids collected in the 2012 growing season, a fourth B. cockerelli haplotype was discovered corresponding to the Southwestern United States geographical region. High-resolution melting analyses identified this new haplotype using an amplicon generated from a portion of the B. cockerelli mitochondrial cytochrome coxidase subunit I gene. Sequencing of this gene, as well as use of a restriction enzyme assay, confirmed the identification of the novel B. cockerelli haplotype in the United States.

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