THE EFFECTS OF WEED STRIP-MANAGEMENT ON PESTS AND BENEFICIAL ARTHROPODS IN WINTER-WHEAT FIELDS

To find out if winter wheat is infested with pests insects from sown w eed strips and if beneficial arthropods enhanced by weed strips could decimate pests efficiently near them, strip-managed winter wheat field s and one field without a strip were investigated. Ar different distan ces from the weed strips and from the field edge, respectively, pest i nsects and their antagonists were registered by visual control and by sweep netting in 1993 and 1994. The dominant pest insects were cereal aphids and leaf beetles. The infestation with aphids was always very l ow and did not show any differences between the studied distances from the weed strip. In 1993, the cereal leaf beetles were more numerous i n the field without strip than in the strip-managed ones and at the be ginning of their incidence in 1994, they were significantly more numer ous in the middle of the Field than close to the weed strip. Consequen tly, cereal crop was not more infested with pest insects near a weed s trip than in the rest of the field. Predatory arthropods such as spide rs, Nabidae and Dolichopodidae were found in larger numbers near the w eed strips than in the middle of the Grids. However, parasitic Hymenop tera were mostly equally distributed over the whole fields. The number of aphidophagous predators was not significantly different between th e studied distances in the wheat fields, bur they were often more abun dant in the strip-managed fields than in tile field without a strip. T here were fewer aphids per larvae of syrphids near the sown weed strip s than in the middle of the fields and this predator-prey relationship was also closer and, consequently, better in the strip-managed fields than in the field without a strip. Thus, an enhancing effect of benef icial arthropods by sown weed strips on the adjacent wheat fields and a reduction of pest insects could be shown.