Spatial distribution of different life stages of one Dipteran community along hedgerow and field margin

Flying pattern of Dipteran adults and distribution of larvae in soil and litter were studied using yellow water traps and soil samples, respectively, in four positions near the border of a barley field: in the hedgerow, the grass strip, the field margin (either with perennials or with barley) and the centre of the field. The sampling and trapping covering all seasonal aspects were performed in an agricultural landscape near Venice (Italy). Higher numbers of flying adults were trapped in the field margin and the field; values in the hedgerow and the grass strip were lower. In contrast, the lowest values of larval abundance were found in the field, while values in the extended field margin, the grass strip and the hedgerow were higher. Comparison of extensively used (uncultivated) part of the field margin with intensively used part of the field margin and centre of the field indicated that the increase in larval abundance in the uncultivated margin is caused by reduced cultivation and not by marginal position. According to the spatial distributions of adults and larvae, several groups can be distinguished. The first Dipteran group develops in various habitats and prefers the field as adults, e.g. for hunting (Dolichopodidae). The second group develops in the field (particularly, some pest Chloropidae and Agromyzidae) and occurs there as adults too. Grass strip and hedgerow affect the flight activity of these groups negatively. The third Dipteran group prefers the hedgerow, the grass strip and the field margin as adults. Some of these develop in an extensive strip (Scatopsidae) near the hedgerow and some outside the studied plot (Culicidae). Finally, there are Diptera which develop in the extensive part of the field margin (Chironomidae) and disperse around all investigated habitats.