Abstract. Dubas bug, Ommatissus lybicus Bergevin, is an important pest of date palm on the Arab peninsula. This sucking insect causes great damage to the trees and reduces the quantity and quality of the dates. Effect of temperature on the development of the immature stages of O. lybicus was studied in the laboratory by rearing them at nine constant temperatures, ranging from 15 to 35°C. Development was successfully completed at temperatures ranging from 20 to 35°C for eggs and from 20 to 32.5°C for nymphs. The lower thermal thresholds for development of eggs, nymphs and egg-adult were estimated by means of linear regression as 12.9, 12.9 and 13.2°C, respectively. Thermal units required for the development of the same stages were 572.5, 648.2 and 1184.4 degree-days, respectively. The lethal high temperatures were also estimated using a nonlinear model as 34.5, 43.4 and 34.6°C for eggs, nymphs and total immature stages, respectively. The development rate and survival data indicate that the optimum temperature range for O. lybicus is 25-27.5°C.