YIELD LOSSES IN MATURING SPRING WHEAT CAUSED BY CEREAL APHIDS (HOMOPTERA, APHIDIDAE) UNDER LABORATORY CONDITIONS

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 1st experiment, populations of 30, 60, and 120 aphids of each species were initiated on 'Sharp' spring wheat at the b oot, 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 o f feeding intensity. The 2nd experiment was initiated as in the 1st, b ut the aphid populations were allowed to fluctuate to obtain a range o f cumulative feeding intensities. The results of the 1st experiment sh owed that R. padi 600 and 1,200 aphid-day treatments at the onset of t he boot stage caused grain yield losses of 19 and 31%, respectively. T he 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 boo t stage. Regression analysis of data from the 2nd experiment showed th at only feeding by R. padi caused significant yield loss and only duri ng the boot stage. Reduction in the number of the spikelets per head d uring the boot stage and in the average seed weight during later stage s of plant growth were the principal components of yield loss caused b y the feeding of cereal aphids.