Seasonal abundance of Sitobion avenae (F.) and Rhopalosiphum padi (L.) was monitored in Nova Scotia winter wheat plots, Rhopalosiphum padi was the more common aphid species during "heading out." Winter wheat cultivars differed in their resistance to R. padi development; the highest reproductive rate was on 'Absolvent.' The effect of chemicals used in intensive cereal management on R. padi and Coccinella septempunctata (L.) was assessed. Dimethoate and carbaryl caused similar high mortality to both insects, but pirimicarb was more toxic to the aphid than to its predator. Over a 2-year period, field plots that received regular pirimicarb treatments for selective aphid control early in the growing season showed a 9% increase in wheat yield, compared with the checks and plots that received carbaryl, Wheat yield increased 18% when pirimicarb was used later in the season; when applied in both periods, pirimicarb gave a total yield increase of nearly 30%. Late applications of carbaryl alone, or in combination with pirimicarb, increased yields by only 9% over the controls. Half of the yield increase (18% vs. 9%) with late season control by pirimicarb was lost with the addition of carbaryl, which minimized the C. septempunctata population for nonselective insect control. Rhopalosiphum padi numbers from June 20 to July 15 had the greatest impact on yield in these plots, and natural control agents including C. septempunctata accounted for a 9% increase in yield.
