Voltinism of the European corn borer, Ostrinia nubilalis Hbn., in Poland

From 1992 to 1996 the voltinism of the European com borer, Ostrinia nubilalis Hbn., was investigated in Poland. During the study, over 6000 larvae were collected in maize stalks in autumn. In 1994, pupal cases were observed in stalks. This indicated the development of second generation adults of the pest. Pupal cases were not found in other years of the study. The difference between 1994 and the other years was found when the degree-days accumulation at base 10°C was calculated for the periods between July 1 and July 19 (daylight 15 hrs 58 min), or July 29 (daylight 15 hrs 32 min). These values were highest in 1994 and reached 246.5°C, or 414.0°C respectively. The results indicate that degree-days accumulation during the whole year is not responsible for the development of the second generation. It appears that high temperatures in July (not only at the beginning, but also at the end) influenced the development of the second generation of 0. nubilalis in Poland. Average July daily temperatures in 1994 were extremely high (24.5°C). Such temperatures can allow a small partial development of the second generation of O. nubilalis at a relatively cold location like Wroclaw in Poland with a standard annual mean temperature of 8.3°C.