Selection for a moderately insecticide resistant clone of Myzus persicae (Hemiptera : Aphididae) on sugarbeet in the absence of pesticides

Highly resistant and extremely resistant clones (R-2 and R-3) of Myzus pers icae (Sulzer) exhibited a significantly lower mortality and developed a del eterious dark stomach deposit less frequently on sugarbeet than a susceptib le (S) clone. After allowing equal populations of four resistant clones to develop together on sugarbeet for four weeks, approximately half of the aph ids recovered were from the moderately resistant (R-1) clone, suggesting th at this clone had a significantly greater reproductive rate than the others . There was no significant difference in the propensity of any clone to pro duce alates on sugarbeet, although none of the clones produced very many. I t is suggested that, even in the absence of insecticides on sugarbeet, resi stant clones may become dominant due to their higher fecundity (R-1 clones) and lower mortality (R-2 and R-3 clones) than susceptible clones.