Effects of different intensities of fertilisers and pesticides on aphids and aphid predators in winter wheat

Abstract

The population dynamics of cereal aphids and some aphid predators were compared in winter wheat fields of farming systems with different inputs. Aphid and predator densities were estimated using visual counts (150 tillers per plot) and D-VAC suction trap. In 1992 an aphid gradation occurred with large differences in aphid density between farming systems. In a plot without insecticide under intensive farming, aphids reached a peak density of up to 300 aphids per tiller. Aphid abundance was much lower under integrated (150 aphids per tiller) and extensive (80 aphids per tiller) systems. The decrease in farming intensity was clearly related to lower infestations of wheat plants with Metopolophium dirhodum (Walker), but not with Sitobion avenae (Fabricius). The abundance of the latter was only regulated by insecticide applications. Few aphid-specific predators occurred late in the vegetation period. It seems probable that the missing synchronisation of syrphid oviposition with the beginning of the increase of aphid abundance was the main cause for the high aphid infestation.