BENEFICIAL DIPTERA IN-FIELD CROPS WITH DIFFERENT INPUTS OF PESTICIDESAND FERTILIZERS

Diptera were caught from 1989 to 1992 on an arable field using emergen ce traps. Since 1982 the field had been subdivided into four plots (I- 0-I-3) treated with increasing amounts of pesticides and inorganic fer tilizer (I-1-I-3), or no pesticide and only a minimum of fertilizer (I -0). There was a crop rotation of sugar beet (1989 and 1992), winter w heat (1990) and winter barley (1991). In addition to the field catches , dead leaves sampled before harvest and crop residues were kept in la boratory emergence traps, as well as droppings of mice and hares, whic h had been exposed in the field, to obtain Diptera whose larvae develo p in these substrates. More than 30 species belonging to 15 families w ere thus reared, most of them from sugar beet substrates. The highest numbers of individuals were reached by Sciaridae, particularly the spe cies Lycoriella fucorum (FREY, 1948), which developed in every kind of substrate. Some of the other species were more or less restricted to one substrate. The results of the field catches show that in the sugar beet crop the emergence rates of the most abundant species of Sciarid ae and Phoridae, as well as the family Cecidomyiidae, decreased with i ncreasing rates of agrochemical usage. In the cereal crops, the reacti ons of these taxa to increasing input of pesticide and fertilizer were more diverse. This is also true for the most abundant species of Dros ophilidae and Hybotidae for all crops.