An experimental study aimed to clarify the seasonal cycle of three species of lithosiid moths was conducted under laboratory and field conditions. Miltochrista miniata and Lithosia lurideola have winter diapause, and L. sororcula overwinters as pupae. The diapause in all three species is controlled by day length. The tendency to diapause induction is very strong under all photoperio-dical conditions. In correspondence with the experimentally determined parameters of photoperiodical response (PhPR) the short day for them occurs already in July and thus the caterpillars develop under the short day conditions throughout large part of their life. This causes univoltine seasonal cycle in the investigated species despite of the PhPR.