The effect of bio-dynamic and conventional (= intense) agriculture management on the structure of the spider fauna in cereal fields and on the activity densities of dominant Erigoninae and Lycosidae species was compared in a 4-years-study in the Niederrheinische Bucht, F. R. G. The percentage of the two species most commonly sampled (Oedothorax apicatus and Erigone atra, both Erigoninae) was 66% on bio-dynamic and 81% on conventional fields. Their activity densities on conventional fields were usually higher than on the corresponding bio-dynamic fields. In contrast, all other spiders were more common on bio-dynamic fields. 11% of the spiders sampled on biodynamic fields were Lycosidae; on conventional fields, species of this family became almost extinct (2%). The dominant Lycosidae was Pardosa amentata. Most species of Lycosidae were largely restricted to the field-edges, only Pardosa prativaga invaded the field-centers in higher numbers. It is concluded that the occurence of Lycosidae in arable land depends on agricultural management as well as on the presence of nearby undisturbed areas.
From the results it might be concluded that the potential prey impact of spiders on Aphidina and Collembola is not reduced on conventional fields compared with bio-dynamic fields, but the prey impact on somewhat larger insects must be extremely low. For conservating a diverse spider fauna on arable land, it is necessary to reduce the application of pesticides and to support the colonisation of spiders into cereal fields. To it the size of the fields should be rather low and the fields intermixed with undisturbed areas.