Two species of leaf beetle (Oulema spp.) – Oulema melanopus (Linnaeus 1758) and Oulema gallaeciana (Heyden 1870) are classified as the pests of cereals of economicalimportance in Poland. Determination of the optimalperiod of their control is very difficult due to extended time of laying eggs and brood of larvae. Mass brood of larvae of both species takes place at the time when larvae hatched from first laid eggs reached ca. 4 mm length of both species. Both developmental stages indicate an optimal term of leaf beetle control. To improve short-term forecasting and warning system the data on developmental cycles of both species from an egg to larva (ca. 4 mm size), the studies were carried out in the field trails in the Wielkopolska region and some in an environmental growth chamber.