Flight patterns of Chironomidae and Dolichopodidae (Diptera) in a suburbanfallow area: the effect of vegetation mosaic

To evaluate the effect of vegetation pattern on the flight pattern of Chiro nomidae and Dolichopodidae, yellow water traps were exposed in five types o f vegetation forming vegetation mosaics in a suburban fallow from March to November 1994. A total of 19 species of Chironomidae and 21 species of Doli chopodidae were recorded. During the sampling period, two peaks of flight c ould be distinguished, the; first in spring and the second in late summer/a utumn. The spring peak was formed by Smittia atterima, Bryophaenocladius il limbatus and B. cf. virgo (Chironomidae) and Campsicnemus scambus, C. curvi pes and Chrysotus gramineus (Dolichopodidae). The autumnal peak was formed by S. atterima (Chironomidae) and Medetera mixta (Dolichopodidae). The flig ht activity of both Chironomidae and Dolichopodidae was highest in patches with open and low vegetation and lowest in high and dense vegetation. A sig nificant reduction appeared even on the border of high vegetation. The Spea rman rank correlation of dominant species and the PCA of community structur e and environmental variables indicated that vegetation height, litter and shading negatively affected the density of flying specimens, whereas distan ce from high vegetation edge and bare soil cover had a positive effect. The se trends were similar in both spring and autumnal peaks of flying activity . The results indicated that the decision about the direction of flight are affected by both "horizontal view" and local "vertical view" information. The relative importance of these information sources may vary among the inv estigated groups.