SYRPHIDS AS NATURAL ENEMIES OF CEREAL APHIDS IN GERMANY - ASPECTS OF THEIR BIOLOGY AND EFFICACY IN DIFFERENT YEARS AND REGIONS

An evaluation was made of the influence of aphidophagous syrphid larvae on the population dynamics of cereal aphids in winter wheat in Germany, using both field records and published information. The peak density of aphid populations was significantly dependent on aphid abundance at the time syrphid larvae became active, a fact indicating the high predation potential of the beneficials as well as the importance of synchronisation. The level of aphid infestation was generally lower in southern than in northern Germany. This difference may result from syrphid larvae being 2-3 weeks earlier in southern Germany, when aphid numbers were only half those found in northern Germany.