ABSTRACT
The influence of insecticide treatments on cereal aphids and aphid specific predators was investigated in field and laboratory studies from 1983–1986. In the majority of years an increase of aphid density above the economic threshold could be observed late in the season at growth stage 69. Under these circumstances spraying with Pirimor (Pirimicarb) and Sumicidin (Fenvalerate) in reduced dose rates was sufficient to prevent yield losses and to achieve a better economic return. In addition, the selective properties of Pirimor and Sumicidin for coccinellid and syrphid larvae could be further increased by this modified application procedure. Apart from direct toxic effects often a long term reduction of aphid-specific predators occurred even after treatment with selective aphicides as a result of the complete elimination of aphids. Starvation then became a main mortality factor. These detrimental effects can be avoided only to a certain degree if the efficacy of used aphicides is reduced. Again, the choice of appropriate dose rates offers the possibility to maintain limited aphid populations in the field as an essential food source for these predators.
