At the season peak, numbers in 1996 and 1996-97 were three and one and a half times higher, respectively, than in the first year. Peaks presumably reflected emergence of adult flies from the previous year s pupae that overwintered in the soil. Five of the eight species showed a second peak about four weeks after the first. The second peak most likely reflects emergence of a second generation. Rainfall and wind run were less important.
Further work is required to provide robust indicators of potential rises in fly numbers.