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Résumé :
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Populations of the English grain aphid, Sitobion avenae (F.), and the bird cherry-oat aphid, Rhopalosiphum padi (L.), develop in some years on maturing wheat, Triticum aestivum (L.), in the Dakotas and western Minnesota. Two experiments were conducted under controlled conditions to determine the yield loss caused by these aphids late in the growth cycle of wheat. In the 1 st experiment, populations of 30, 60, and 120 aphids of each species were initiated on 'Sharp' spring wheat at the boot, anthesis, and dough stages of plant growth and regulated at those numbers over a 10-d period to obtain 300, 600, and 1,200 aphid-days of feeding intensity. The 2 nd experiment was initiated as in the 1 st, but the aphid populations were allowed to fluctuate to obtain a range of cumulative feeding intensities. The results of the 1 st experiment showed that R. padi 600 and 1,200 aphid-day treatments at the onset of the boot stage caused grain yield losses of 19 and 31%, respectively. The 300, 600, and 1,200 aphid-day treatments during the anthesis stage of plant growth caused yield losses of 14, 15, and 20%, respectively. Feeding by S. avenae caused significant yield loss only during the boot stage. Regression analysis of data from the 2 nd experiment showed that only feeding by R. padi caused significant yield loss and only during the boot stage. Reduction in the number of the spikelets per head during the boot stage and in the average seed weight during later stages of plant growth were the principal components of yield loss caused by the feeding of cereal aphids.
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