THE SUSCEPTIBILITY TO MALATHION OF METOPOLOPHIUM-DIRHODUM ON 2 WHEAT SPECIES AT 2 GROWTH-STAGES, AND THE EFFECT OF PLANT-GROWTH REGULATORS ON THIS SUSCEPTIBILITY

Malathion tolerance of the rose-grain aphid Metopolophium dirhodum (Wa lker) reared on the ancient wheat variety Emmer (Trilicum dicoccum L.) was tested by topical bioassay and found to be lower than that of aph ids reared on the modern more susceptible variety Maris Kinsman (T. ae stivum L.). On both varieties, tolerance was greater at stem elongatio n than at the tillering stage of plant growth. All statistically signi ficant differences when plants were treated with Cycocel and MCPA show ed that the two chemicals, respectively, reduced and increased aphid t olerance to malathion, in keeping with the effects of the chemicals on induced plant resistance to aphids reported in the literature. Probit mortality slopes were not progressively altered by changes in LC50, s o that similar differences in aphid tolerance to malathion were found at both LC50 and LC90 levels.