The tomato–potato psyllid Bactericera [Paratrioza] cockerelli (Sulc) has recently caused losses exceeding 50% on fresh market tomatoes in California and Baja, Mexico by injecting a toxin that results in a condition known as ‘psyllid yellows’. The objectives of this study were to: (i) document oviposition preferences on a range of tomato cultivars; (ii) determine threshold levels for psyllid densities that would cause psyllid yellows on tomatoes within the first three weeks following transplanting; and (iii) identify the most important ‘psyllid yellows’ symptoms that might be used in surveying and monitoring for this pest. Plant lines tested included the commonly-planted commercial cultivars ‘Shady Lady’ and ‘QualiT 21’, an older, previously commercial cultivar ‘7718 VFN’, a common cultivar planted by consumers ‘Yellow Pear’, and a wild type plant accession, PI 134417. When given a choice, psyllids significantly preferred ‘Yellow Pear’ and avoided PI 134417 for oviposition. Under no-choice conditions psyllids laid significantly fewer eggs on PI 134417, but all the other plant lines were equally good substrates for laying eggs. Thus, oviposition preference is not likely to provide a functional management strategy in large plantings. On ‘Shady Lady’, psyllids preferred to oviposit on plants already infested with adults. On both ‘Shady Lady’ and ‘7718 VFN’ oviposition was significantly greater on plants previously infested by nymphs as compared to uninfested control plants. This suggests that, at least for some cultivars, there is a physiological change in plant attractiveness following psyllid feeding. ‘Yellow Pear’ and ‘QualiT 21’ were relatively tolerant of psyllids, requiring 18 nymphs per plant to produce the disease symptoms. Only eight nymphs per plant were needed on ‘Shady Lady’ and ‘7718 VFN’. For all cultivars, the pest density showed strong correlations with measurements such as the number of yellowing leaves and leaflets and distorted leaves, which were as good as or better than the first factor extracted from principal component analysis. Therefore, such measurements have the potential to simplify field surveys.
