The biology and ecology of three codling moth, Cydia pomonella L. (CM), populations from Croatia were investigated. The effects of current and past climate regimes on the behaviour of the three CM populations were investigated, and the changes in their biology and ecology were observed. The first population investigated was free from chemical control treatment, whereas the other two populations were subjected to chemical control. Climate data were obtained from LUFT climatological stations in Croatia. A later emergence of adult moths in the spring, later oviposition and later emergence of larvae occurred in the untreated orchard versus the treated orchards. In the untreated orchard, two generations of CMs were observed per year, whereas an additional third flight period of the moths was observed in the treated orchards. The results of this study confirm the possibility that a third generation of the pest can develop in Croatia in years in which the sum of degree-day is higher than average.