The present work was conducted to study the relationship between the developmental stages of the predator Nephus includens (Kisch) (Coleoptera: Coccinellidae) and the required thermal units at three constant temperatures, (20, 25 and 30ºC) on certain  mealy bug species (Planococcus citri Risso, Icerya seychellarum (Westwood) and Maconellicoccus hirsutus (Green).         The results indicated that, the duration of the predator was longer at 20ºC. As temperature increased from 20-30ºC the longevity decreased, the lower thermal threshold for the development of N. includens 10.9, 10.6 and 11.1ºC for eggs , 6.4, 2.1 and 0.7ºC for larvae, 8.4, 5.6 and 11.9ºC for pupa while it were 0.1, 3.2 and 1.9ºC for the total duration from (egg to adult). The heat units requirement for the development of eggs were 90.1, 92.4 and 91.5 DD's , for larvae were 387.7, 328.1 and 382.5 DD's, for the pupa  325.8, 308.1 and 390.1 DD's  while it were 713.8, 674.2 and 765.3 DD's for the  development period of P. citri, I. seychellarum and M. hirtsutus  respectively. The lower  thermal threshold for longevity (female and male) of N. includens were 12.8 & 18.4, 10.9 and 13.2&  22.8  & 48.7, meanwhile, the heat units requirement for longevity of (female and male) were 2779.8 & 2513.7, 2709.9 and 2380.7 & 2432.4 & 4206.2 on the same mealy bug species, respectively. The average of total consumption per larva was the highest at 25 + 1ºC and when this predator fed on the mealy bug species P. citri during its larval stage.          The results revealed that, the longevity of the predator adult stage decreased with increasing the temperature degrees. The highest consumption rate per female was at 30 + 1ºC comparing with the other temperature degrees. The number of deposited eggs per female was the highest (185.74 + 1.92 eggs) when female reared on P. citri at 25 + 1ºC. Obtained results provide essential information for predicting the field population of the predator N. includens, releasing time on certain mealy bug species for controlling these pests and it's recommended to be an item of Integrated Pest Management Programs in Egyptian field designed to control certain mealy bug species.