Asiatic originated Pseudococcus comstocki (Kuwana), the Comstock mealybug (Hemiptera: Pseudococcidae) is polyphagous cosmopolite species. Nowadays it is spreading through to Europe and becoming wide distribution. In this study, the developmental time, survival and fecundity of P. comstocki on two mulberry species (Morus alba and M. nigra) (Moraceae) were studied at four different temperatures (18 +/- 1, 23 +/- 1, 28 +/- 1 and 20-32 degrees C) and thermal constant was calculated. According to results, it appears that performance of P. comstocki and, consequently, its population increase were affected by feeding with different mulberry species and at different temperatures, and M. nigra seems to be more likely susceptible to the mealybug than M. alba in each temperatures because it displayed the highest performance on this host plant. The results showed that the population on M. nigra (r(m) = 0.123 female/female/day; R-0 = 108.933 female/female; T-0= 38.160 day; DT= 5.639 day) developed better than that on M. alba (r(m)= 0.115 female/female/day; R-0= 84.281 female/female; T-0= 38.600 day; DT= 6.032 day) at 28 degrees C. It was found that there was an inverse relationship between the growth period of the population and the temperature, development of the mealybug becoming fully grown was the fastest on both Morus species at 28 degrees C. The threshold for development (t) and the thermal constant (ThC) of the mealybug on M. nigra was determined as 7.87 degrees C, K = 513 degree-days respectively; while on M. a/ba, these parameters were found to be 7.76 degrees C and K = 518 degree-days respectively.