COMPARATIVE BIOLOGY OF POTATO PSYLLID, BACTERICERA COCKERELLI (HEMIPTERA: TRIOZIDAE) HAPLOTYPES
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Zebra chip, a new and economically important disease of potato, is threatening potato production in the United States, Mexico, Central America, and New Zealand. The disease is associated with the bacterium `Candidatus Liberibacter solanacearum' (Lso), vectored by potato psyllid, Bactericera cockerelli (Sulc) (Hemiptera: Triozidae). This insect pest feeds on over 40 plant species, including cultivated and wild solanaceous plants. Recent discoveries of four genetic variants (haplotypes) of potato psyllid, coupled with the finding that it overwinters in the Pacific Northwest on bittersweet nightshade (Solanum dulcamara), may complicate management of this psyllid, if differences exist in biological traits among the haplotypes. The present study compared development and reproduction among three psyllid haplotypes (Central, Western, and Northwestern) commonly found on Pacific Northwest potato crops, when reared on potato or bittersweet nightshade. Lso transmission efficiency among the three haplotypes was also assessed. The results showed that development time was longer for psyllids reared on nightshade than potato. The duration of the pre-oviposition period, egg incubation requirements, nymphal development time, and total developmental time was higher on bittersweet nightshade compared to potato. The largest host effects were found for the Central haplotype, which exhibited an extended 5 d preoviposition period on bittersweet nightshade compared to potato. Fecundity differed significantly among haplotypes, with an average lifetime fecundity of 1050, 877, and 629 eggs for Northwestern, Western, and Central females, respectively. Egg hatch was significantly reduced in psyllids reared on nightshade. Adult psyllids lived longer on nightshade than on potato. Females of the Northwestern haplotype failed to produce viable eggs when mated by males of either the Western or Central haplotypes, suggesting partial interhaplotype incompatibility. The stylet probing behaviors and Lso transmission efficiency of the three haplotypes were similar, suggesting that the psyllids probe and feed in a similar manner. However, Lso transmission rate for each of the psyllid haplotypes significantly increased with inoculation access period. The minimum inoculation time required for successful infection of potato plants with Lso was less than 10 min. Information from this research increases understanding of potato psyllid biology and will help to develop effective management strategies for zebra chip.