a1 AFRC Institute of Arable Crops Research, Rothamsted Experimental Station, Harpenden, Herts., UK
Residues of pirimicarb or deltamethrin plus heptenophos on potatoes in field cages in southern England reduced artificial infestations of susceptible and insecticide-resistant strains of Myzus persicae (Sulzer) introduced up to 14 days after treatment. Deltamethrin plus heptenophos gave better control than pirimicarb, particularly of nymphs, but also selected more strongly for very resistant (R2) aphids. Susceptible (S) aphids survived the treatment with deltamethrin plus heptenophos better than moderately resistant (R1) aphids, probably due to a different or more pronounced behavioural response to the pyrethroid. However, the combination of the greater persistence of deltamethrin plus heptenophos and the high resistance of M. persicae to the pyrethroid led to more prolonged selection for R2 aphids, which is sometimes associated with a resurgence in aphid numbers.
(Received June 01 1987)
c1 To whom correspondence should be addressed.
p1 Present address: Entomology Department, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, UK.