COMPARISON OF 2 GREENBUG (HOMOPTERA, APHIDIDAE) CLONES BY NUMERICAL INCREASE AND VIRULENCE PROCEDURES ON 8 SMALL GRAINS

Clones of greenbug, Schizaphis graminum (Rondani), biotypes J and E we re investigated for numerical increase and damage to eight small grain s. The small grain cultivars were: 'Triumph 64' and 'Dickinson 28A' wh eat; 'Wintermalt' and ;Post' barley; 'Elbon' and 'Insave F. A.' rye; a nd 'Nora' and CI 1580 oat. On the 18th d after infestation at 17:15-de grees-C and a photoperiod of 15:9 (L:D) h., J differed from E by a gre ater density per plant on 'Post', 'Wintermalt', and CI 1580 but had a lower density per plant on 'Nora', 'Dickinson 28A', 'Triumph 64', 'Ins ave F. A.', and 'Elbon'. The plant damage ratings after 21 d demonstra ted clear differences between the greenbug clones. Differences among c ultivar responses to clones remained the same at four different temper ature and photoperiod regimes. 'Dickinson 28A' and 'Post' were the mos t consistent in distinguishing greenbug clones E and J. Damage ratings were correlated with the numbers of aphids per plant on specific cult ivars. Clone J from the barley growing region of Idaho had greater den sities and caused more damage than clone E on the barley cultivars, bu t clone J had fewer progeny and caused less damage than clone E on the wheat and rye cultivars.