Duration of exposure to potato psyllid, Bactericera cockerelli (Hemiptera: Psyllidae), affects expression of zebra chip defect in potatoes

The role of the potato psyllid, Bactericera cockerelli (Sulc), in symptom expression of zebra chip, a new and emerging potato disease in southwestern United States, Mexico, Central America, and New Zealand, was investigated in central Washington from April to August 2008 under field conditions. Healthy potato (Solanum tuberosum) plants were planted in small field cages and potato psyllids were introduced in the cages and allowed to feed and establish on the plants for periods of 1, 3, 7, 14, and 30 days; additional treatments included cages in which psyllids were allowed to feed on healthy potato plants for the entire duration of the experiment, and a control treatment that consisted of caged psyllid-free potato plants. Psyllids were removed from the designated cages following psyllid exposure with insecticides. Plants were monitored for psyllid damage and zebra chip symptoms. Results showed that plants exposed to potato psyllids exhibited typical zebra chip symptoms, including chlorosis, short internode, leaf scorching, and early plant decline. At harvest, potato tubers were checked for zebra chip symptoms and the disease incidence was estimated. Results showed that 100% of caged potato plants exposed to psyllids produced tubers with typical zebra chip symptoms whereas the psyllid-free caged plants did not exhibit the disease symptoms. It was also concluded that zebra chip causal agents could be transmitted to healthy plants by the potato psyllid in a period of time as short as one day of insect exposure.