Potential movement on surface airflow of a bivoltine population of European corn borer (Pyralidae: Lepidoptera) into a historically univoltine habitat

Larval collections of European corn borer, Ostrinia nubilalis (Hubner),were made in and surrounding a seed corn nursery at Johnstown, ND, a year before and each of 3 yr during a test for hybrid resistance to this insect. Johnstown is in an area known to maintain a univoltine population of O. nubilalis . The 30,000 inbred corn plants tested for resistance, however, were infested each year with a bivoltine population of O. nubilalis . Each sample site collection was maintained as a separate population, and the 2nd laboratory-reared generation was tested for diapause frequency in growth chambers programmed to force most univoltine individuals to enter larval diapause and allow a minimum of 50% of bivoltine individuals to continue development. These results illustrate that bivoltine populations dispersed at least 32 km/yr. The results indicate further that light southerly or easterly surface winds (under 8 km/h) were the essential transport mechanisms for this dispersal. It is probable that bivoltine O. nubilalis have been invading the historically univoltine areas of northwestern Minnesota, North Dakota, and the Canadian prairie provinces from the south for years.