This investigation was carried out in laboratory at Vegetable Research Pests Dep. Plant Protection Research Institute Dokki,Giza.. To evaluate the effect of three temperatures (20, 25 and 30ºC) on the biological aspects of Phthorimaea operculella(Zell.) Threshold of development (t) and accumulated heats (k) for total preimaginal development of P. operculella were calculated to be 4.9 ºC and 741.7 degree-days (DD`s). Development of egg stage required 68.66 dd`s above 8.6 ºC while larval stage demanded 451.2  dd`s  above  5.8 ºC  and this value 138.2 dd`s above 10.03   ºC for adult stage. Accumulation of 782.1 dd`s were sufficient for the completion of onegeneration.The accumulatedthermal heat units (T.U.) or effective degree-days estimated through insect activity time The aim of this part of investigation is to establish the velocity constants (i.e the relationship between temperature and speed of development).