RELATIONSHIP BETWEEN NUMBER OF GREENBUGS (HOMOPTERA-APHIDIDAE) AND DAMAGE TO WHEAT SEEDLINGS

Investigations of plant resistance to greenbugs in the laboratory and greenhouse require sufficient plant damage to show susceptibility but not allow damage to become critical. This study was conducted to deter mine the minimum number of greenbugs per plant needed to significantly damage susceptible wheat seedlings. Ten or more greenbugs feeding on susceptible wheat seedlings for 14 days (140 cumulative aphid days) we re required to reduce growth components to the point that they differe d significantly from the controls. Root dry weight was the most sensit ive plant measure of greenbug damage. Root fresh weight values also sh owed significant differences (P<0.05) but were more variable than dry weights. Regression analysis indicated a linear relationship with a ne gative slope between the numbers of greenbugs per plant (cumulative ap hid days) and all measurements of seedling growth. Root fresh weight, root dry weight, total root length, and shoot dry weight were highly c orrelated with infestation level.