Stanislav GOMBOC and Lea MILEVOJ
Biotechnical Faculty, Agronomy Department, Institute of Phytomedicine, Jamnikarjeva 101, SI-1000 Ljubljana

During several years of studying bionomy and strains of European corn borer (Ostrinia nubilalis) by light traps and visual examination of development stages on maize, considerable differences have been observed in the time of its appearance and in the number of its generations in Slovenia. In Nova Gorica (near the Italian border) two generations per year were observed during a three-year study. The first one starts in the middle of May and lasts till the beginning of July, while the second one starts in the end of July and lasts till September (its maximum being in the beginning of August). European corn borer shows a very similar bionomy in the Southern part of Slovenia, where equally two generations develop each year. In the central and Eastern part of Slovenia European corn borer develops only one generation per year, this being rather long, as moths appear unevenly from the end of May till August. In order to determine if the number of generations depends on climatic conditions two populations of European corn borers - one from Prekmurje (near Hungarian border) and one from Nova Gorica - were observed under the same conditions in greenhouse with net cower on the Biotechnical faculty in Ljubljana. During this one-year study of bionomy under natural conditions it was found out that the population from Nova Gorica developed two generations per year also under somewhat colder conditions, while the population from Prekmurje had only one generation yearly. The bionomy of the population from Primorje coincided in time with the bionomy of the same population in the natural habitat which is an even greater surprise. The up to now two-year study of European corn borer strains with pheromone traps did not give satisfactory results. In Bilje, where two generations develop each year, the E and Z strains are equally common, in central Slovenia the E strain is more usual, while the Z strain is the only one found in the Eastern part of Slovenia along the Hungarian and Austrian border. The Z strain develops only one generation under the conditions in Slovenia, the same is true for the E strain in the central part of Slovenia. The results on the European corn borer strains in Slovenia are identical to those obtained by researchers in the neighboring countries bordering with Slovenia. Key words: European corn borer, Ostrinia nubilalis, bionomy, strains, monitoring, Slovenia.