In 2018-2020 phenological observations of Cydalima perspectalis Walker were carried out in two agroclimatic regions of the Crimea. The pest, both on the Southern Coast of the Crimea and in the central foothill zone, develops in three generations. The sum of effective temperatures required for the development of generations varies over the years in a wide range, which is due to the asynchronous development of the caterpillars of C. perspectalis . The beginning of summer of the adults of the overwintered generation over the years of research in both regions differed insignificantly and was noted with the accumulation of the sums of effective air temperatures above 10°С on the Southern Coast of the Crimea from 210 to 297 degree days, and in Simferopol - from 222 to 299 degree days. It was found that in the summer months in the central foothill zone of the Crimea, in terms of temperature indicators, more favorable conditions are created for the development of boxwood firewood than on the Southern Coast of the Crimea. The combination of hydrothermal conditions, in which air temperatures exceed 33-36°C, and the relative humidity drops below 19-49%, cause the death of up to 20-28% of Cydalima perspectalis egg embryos at an early stage of embryogenesis. From the embryos of eggs of later stages of embryogenesis, under these conditions, the hatching of caterpillars occurred by 100%.