YIELD OF SPRING WHEAT IN RELATION TO LEVEL OF INFESTATION BY GREENBUGS (HOMOPTERA, APHIDIDAE)

The effect of greenbug, Schizaphis graminum (Rondani), infestations on yield components of early- and late-planted spring wheat, Triticum ae stivum L., were measured in 2 successive years in eastern South Dakota . Greenbug populations in plots generally increased rapidly and peaked when wheat plants were in boot stage. Populations then began a steady decrease until anthesis, at which time they were near zero. The numbe r of seeds per spikelet and the number of spikelets per square metre w ere consistently significantly negatively correlated with aphid-days, whereas average seed weight was significantly negatively correlated wi th aphid-days for only one planting. A linear regression model that in cluded different intercepts for each spring wheat planting and a commo n slope relating yield to greenbug feeding days (aphid-days) provided a good fit to the data. Based on the model, a loss of 41 kg of grain p er hectare is expected for each 100 aphid-days that accumulate per til ler.