The susceptibility to malathion of Metopolophium dirhodum on two wheat species at two growth stages, and the effect of plant growth regulators on this susceptibility

Abstract

Malathion tolerance of the rose-grain aphid Metopolophium dirhodum (Walker) reared on the ancient wheat variety Emmer (Triticum dicoccum L.) was tested by topical bioassay and found to be lower than that of aphids reared on the modern more susceptible variety Maris Kinsman (T. aestivum L.). On both varieties, tolerance was greater at stem elongation than at the tillering stage of plant growth. All statistically significant differences when plants were treated with Cycocel and MCPA showed that the two chemicals, respectively, reduced and increased aphid tolerance 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, so that similar differences in aphid tolerance to malathion were found at both LC50 and LC90 levels.