The potential of leys and short rotation coppice hedges as reservoirs for parasitoids of cereal aphids in organic agriculture

The aim of this study was to assess whether leys used for nitrogen fixation and fodder, which cover from a fifth to more than half the acreage on orga nic farms, as well as short rotation coppice (SRC) used for energy purposes , have potentials as reservoirs for aphid parasitoids in organic agricultur e. Exposure of cereal aphids to naturally occurring parasitoids in various crops showed that parasitoids capable of parasitizing the pest aphid Sitobi on avenae were active in ley, alfalfa and SRC from spring to late autumn, b ut in barley fields only in mid-summer. Parasitism by Aphidius sp. dominate d in ley, whereas parasitism by Praon sp. was most frequent in SRC. Alterna tive aphid hosts for parasitoids of S. avenae were shown to be present in l ate summer, late autumn and early spring in ley and SRC. Within field distr ibution of parasitism and prevalence of entomophtoralean fungi on aphids in spring barley fields were determined by spatially explicit sampling, but w as not consistently affected by proximity to ley or SRC. The data indicate that SRC hedges and clover/grass leys in the rotation may increase diversit y and activity of parasitoids attacking cereal aphids. (C) 2001 Elsevier Sc ience B.V. All rights reserved.