The detection and distribution of organophosphorus and carbamate insecticide-resistant Myzus persicae (Sulz.) in Britain in 1976

TLDR: The dip-test, a simple, rapid and inexpensive bioassay designed to detect resistance and its different levels gave satisfactory results which warrant its use where biochemical detection of resistance is not possible.

Abstract: Examination of the enzyme that determines the level of resistance to organophosphorus insecticides and carbamates in Myzus persicae (Sulz.) and bioassays were used to establish the frequency and resistance levels of resistant aphids on outdoor crops in Britain in 1976. The biochemical tests, staining esterase-4 after electrophoresis and total esterase determination, were more sensitive than bioassays. However the dip-test, a simple, rapid and inexpensive bioassay designed to detect resistance and its different levels gave satisfactory results which warrant its use where biochemical detection of resistance is not possible. Carboxylesterase activities of M. persicae collected in 1976 fell into three groups: low, moderate and high, and these were correlated with differences in tolerance to dimethoate, demeton-S-methyl and pirimicarb. Aphids with low esterase activity were susceptible(S). Those with the moderately active enzyme (R1) had five- to seven-fold resistance to the two organophosphorus insecticides and were marginally resistant (about two-fold) to pirimicarb. The insects with the most active esterase (R2) were strongly resistant to dimethoate (resistance factor, RF × 126) and moderately resistant to demeton-S-methyl (RF × 17) and pirimicarb (RF × 8). Some R1, but no S aphids survived the recommended dose of demeton-S-methyl on field crops probably because they were under the lowest leaves and therefore protected from direct contact with the spray. Laboratory tests demonstrated that these R1 aphids tolerated the residual deposit and systemic dose present in the leaves of the treated potato-plants. This enabled their numbers to recover in treated fields much faster than the susceptible insects which could do so by immigration only when the residual dose in the plant was no longer toxic. R1 aphids were common throughout the country particularly in eastern England where susceptible aphids were rare, but in the Shardlow area of Derbyshire susceptible aphids were in the majority throughout the summer. R2 aphids were found only in samples from the west of Scotland and northern England. The implications of the presence of aphids with different levels of resistance for aphid control are discussed.