Density of adult hoverflies (Dipt., Syrphidae) in sown weed strips acid adjacent fields

In 1992 and 1993, studies examined numbers of adult hoverflies in sown weed strips, adjacent fields and a field boundary in the Swiss plateau, near Bern. Hoverflies were observed quantitatively and were divided according to their larval food. In both years, distinctly more aphidophagous and aquatic hoverflies were observed in the weed strips than in the adjacent fields. Copro- and phytophagous hoverflies were observed in very low numbers acid they were almost entirely confined to the weed strips and the field boundary. The weed strips contained a high density of flowering plants and therefore proved to be very attractive feeding places for all hoverflies. Numbers of aphidophagous hoverflies declined slightly with increasing distance from the weed strips. Possible impacts of weed strips in encouraging aphidophagous hoverflies and their potential as aphid antagonists are discussed.