No abstract

SUMMARYThe pyrethroid, deltamethrin, alone or as an emulsifiable formulation, hindered infection of healthy plants with the persistent beet mild yellowing virus (BMYV) and both acquisition of, and infection with, the non‐persistent potato virus Y (PVY) and the semi‐persistent sugar beet yellows virus (BYV) by Myzus persicae in glasshouse tests.Another pyrethroid, RU‐15525, also protected against infection with PVY. Even sub‐lethal amounts of deltamethrin decreased virus transmission by rapidly incapacitating the aphids, the effect being least with aphids most resistant to organophosphorous insecticides and to certain pyrethroids including deltamethrin. Demeton‐S‐methyl hindered infection only with BMYV. This work shows that deltamethrin restricts transmission of persistent, semi‐persistent and perhaps more importantly of non‐persistent viruses in the glasshouse, and has potential for doing the same in the field.

Structure‐activity relationships (SARs) for 10 pyrethroids against susceptible, kdr and super‐kdr strains of houseflies (Musca domestica L.) were investigated by Principal Components Analysis. In the three strains with kdrLatina' all only slightly to moderately (2.6 to 26‐fold) resistant to pyrethroids, no correlation between the structure and Levels of resistance could be discerned. In flies with super‐kdr, SARs were influenced by the nature of the alcoholic portion of the ester. Resistance was strongest to esters of a‐cyano‐3‐phenoxybenzyl alcohol (74 to 430‐fold) and to permethrin (48 to 55‐fold). It was weak (6.2 to 11‐fold) to cyclopentenone derivatives, being barely stronger than for flies with kdr (2‐6 to 6.3‐fold). Two variants of super‐kdr (3D and A2) were distinguished on the basis of their differential response to esters of 5‐benzyl‐3‐furylmethanol. It is presumed that kdrLatina, super‐kdrA2 and super‐kdr3D form an allelic series in which kdrLatina represents ground level insensitivity, and the two super‐kdrs the progressive extension of strong resistance to more types of ester. The strong differences in resistance to different pyrethroid esters by super‐kdr flies provides scope for improving management of resistance to pyrethroid insecticides and for modifying the SAR of pyrethroids to favour weak resistance.

No 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 (Rz) were strongly resistant to dimethoate (resistance factor, R F x 126) and moderately resistant to demeton-S-methyl (RF x 17) and pirimicarb (RF x 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. Rz 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. 0031-613X/78/0600-0189 502.00 0 1978 Society of Chemical Industry 13 I89