Insecticidal activity of a sugar ester fraction isolated from leaf trichomes of wild tobacco, Nicotiana gossei Domin, to egg, nymph, and adult stages of pear psylla, Cacopsylla pyricola Foerster, was determined in replicated laboratory bioassays. Aqueous solutions of sugar ester concentrations ranging from 62 to 1,000 ppm (mg/liter) were applied by an ultra-low-volume spray device to petri dishes containing eggs, nymphs, or adults. Data were recorded on nymphal mortality rates 1, 3, 5, and 7 d after treatment, on the percentage of eggs hatched 7 d after treatment, on the mortality rates of eclosed nymphs 3 dafter eclosion (10 d after treatment), and on adult mortality rates 1 d after treatment. Mortality rates did not differ significantly for sugar ester concentrations of 500 and 1,000 ppm, which both produced a mortality rate of ≥94% for nymphs and adults 1 d after treatment. Lethal concentration values for sugar esters to pear psylla nymphs and adults differed significantly 1 d after treatment for the LC50 (90 versus 200 ppm, respectively), but not for the LC90 (300 versus 400 ppm, respectively). Nymphal mortality rates for each sugar ester concentration did not increase over time significantly 1 d after application, which suggests that the sugar ester is a contact insecticide that is active mainly in the liquid state. The percentage of eggs hatched was not affected by any of the sugar ester treatments 7 d after application. In contrast, the mortality rates of newly eclosed nymphs ranged from 18.7 to 67% for sugar ester concentrations of 62- 1,000 ppm. Our data suggest that both nymphs and adults would be equally controlled with sugar ester concentrations high enough to obtain a mortality rate of >90%. These results will be useful in determining the range of sugar ester concentrations for field trials. In addition, an inexpensive ultra-low-volume spray device used in the bioassays is described that is capable of applying microliter amounts of candidate insecticidal materials to target insects.