OVIPOSITION AND NICHE PARTITIONING IN APHIDOPHAGOUS INSECTS ON MAIZE

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Abstract
Principal components analysis was used to assess niche partitioning between four aphid predators on the basis of oviposition strategies. The study was conducted by sampling abundance and position of the eggs of these predators in corn monocultures in two locations of southern Quebec. The results indicated that the chrysopid Chrysopa occulata Say laid its eggs on corn leaves usually without aphid colonies, and late in the season. All other predators reacted to aphid concentrations. The syrphid Sphaerophoria philanthus (Mg.) oviposited close to the ground, early in the season, and among colonies of the aphid Rhopalosiphum padi (L.). The two coccinellids laid their eggs during July and August with a maximum during tasseling for Coleomegilla maculata lengi (Timberlake) and after pollination for Hippodamia tredecimpunctata tibialis Say. Of these two species, the latter one selected sites at higher levels on the plant, and was more abundant at the edges of the field. It is suggested that the observed niche partitioning cannot be the result of interspecific competition in variable environments such as maize monocultures.