The box tree moth, Cydalima perspectalis (Walker, 1859) is an invasive pest with a significant impact on the environment and economy. The aim of this research conducted in 2022 was to assess the appearance of adults, length of life, duration of flight, mortality dynamics and population structure in the coastal area and interior of the Split-Dalmatia County. The purpose of the research was to collect developed caterpillars in the areas of Kaštela and Sinj-Brnaze and transform them into adults under semi-field conditions. The results of the research on the dynamics of adult exit and the dynamics of mortality show differences between the researched areas. The emergence of adult butterflies in the Kaštela area starts about 30 days earlier than in the Sinj-Brnaze area. It is clear that there is a difference in the duration of the flight of adults in the researched areas. Thus, in the area of Kaštela, the flight of adults lasts up to 50 days, while in the area of Sinj-Brnaze, the length of the flight is significantly shorter and amounts to 32 days. Research into population structure and gender relations confirmed the presence of two morphological types: the white form and the melanic (brown) form of adult butterflies. The share of the white form in the total population is dominant and varies from 88% (Sinj-Brnaze) to 95% (Kaštela). The share of melanic females is more significant in the area of Sinj-Brnaze and is 9%, while in the area of Kaštela it is 3% of the total population of both sexes. At the same time, the share of melanic males is in the range of 2-3% in both researched areas. It is important to point out the dominance of the share of males compared to females in both areas. Pest control deadlines can be adjusted according to the specifics of the appearance and duration of the butterfly's flight. Thus, in the coastal area of the Split-Dalmatia County, the first treatments should be carried out at the beginning of July, and in the area of Sinj-Brnaze, at the beginning of the second week of August. Detailed data on the flight period and egg-laying are of great importance for pest control.