EFFECTS OF WEED STRIPS ON THE OCCURRENCE OF NOXIOUS COLEOPTERAN SPECIES (NITIDULIDAE, CHRYSOMELIDAE, CURCULIONIDAE)

In 1993 and 1994, the importance of weed strips as reservoir for coleo pteran pests among Nitidulidae, Chrysomelidae and Curculionidae was in vestigated in two weed strips, in fields and the adjacent boundaries w ith the help of yellow traps, suction samples, visual observations and eclectors. During this research, several harmful species were observe d, but always of very low abundance, except the blossom beetles, Melig ethes spp.. They were, first of all, dependent on rape, but after the rape flowering time the new generation was found everywhere searching for food (pollen), especially on yellow flowers such as Sinapis alba i n the strips. Oulema spp., Psylliodes chrysocephala, Leptinotarsa dece mlineata Phyllotreta spp. (Chrysomelidae) and the Ceutorhynchus specie s (Curculionidae) were always connected to their host plant in the fie ld and have only been caught more frequently in presence of the respec tive field. Sitona and Apion weevils also showed low abundance in the strips during both investigation periods. According to these results, weed strips have no enhancing effect on pest species, but in some case s they can offer food resources during the seasonal absence of the cro p, as for the beneficial groups, too. The greatest diversity was revea led in the weed strips, even with rare species for Switzerland. Theref ore, strip-management, providing ecological compensation areas, is an important measure for maintaining species conservation and contributes to biodiversity and sustainable agriculture.