In the climatic conditions of Lower Silesia, Poland the European corn borer lays eggs on sweet corn during 3-5 week period between the 3rd decade of June and the 2nd decade ofAugust. The eggs are laid on leaves L1 to LS ofmain and lateral stems of the plants. Caterpillars start to hatch at the beginning ofJuly, but in 1998-2000 a massive hatching was observed only in the 2nd and in the 3rd decade ofJuly, whereas in 2001 - in the 3rd decade of this month and in the l st decade of August. Larvae are capable of migrating between plant rows on the soil surface, which was observed in 1998-2000 from the end ofJuly till the end of October. Most caterpillars migrated in the 2nd and in the 3rd decade of August and in the first days of September. The cob damage by caterpillars ranged between 31 and 46%. Delayed harvest caused a substantial increase in damage.