Resistance to some organophosphorus insecticides in field populations of Myzus persicae from sugar beet in 1974

Following the failure of insecticides to control Myzus persicae on sugar beet, populations from the field were examined for susceptibility to dimethoate. Topical application of discriminating doses of dimethoate showed a 30‐fold variation in susceptibility between different populations. After this preliminary screening, clones were established from some populations and their resistance determined by both topical application and a systemic bioassay. This confirmed resistance to dimethoate and demonstrated resistance to demeton‐S‐methyl. There was no resistance to some other compounds tested. In all populations tested, resistance was associated with increased carboxylesterase activity.