The relationship between aphid infestations and oviposition by aphidophagous Syrphidae (Diptera)

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Abstract
SUMMARY: Oviposition by aphidophagous Syrphidae varies with the size of aphid infestations and different syrphid species have different optimum aphid population sizes for oviposition.In one experiment using potted brussels sprout plants infested with Brevicoryne brassicae L., Platycheirus manicatus (Meig.) preferred about 100 aphids per plant, P. scutatus (Meig.) about 1000 aphids per plant and Syrphus ribesii (L.) about 2000 aphids per plant. These preferences were less clear in certain Platycheirus species (e.g. P. peltatus (Meig.)), than in Syrphus species (e.g. S. luniger Meig.).Once a plant has been selected for oviposition there may still be selection of suitable colonies on that plant. For a given aphid population, S. luniger preferred a small number of large aggregates to a larger number of smaller ones, whereas S. balteatus (Deg.) preferred the opposite.The tendency of the different species to select aphid populations of different sizes and distributions is likely to decrease interspecific competition.