Detection of insecticide resistance by immunological estimation of carboxylesterase activity inMyzus persicae(Sulzer) and cross reaction of the antiserum withPhorodon humuli(Schrank) (Hemiptera: Aphididae)

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Abstract
An antiserum was prepared against carboxylesterase E4, the enzyme conferring resistance inMyzus persicae(Sulzer) to a wide range of insecticides, and the immunoglobulin G (IgG) fraction was purified from it by affinity chromotography. Interactions of the antiserum and IgG with aphid homogenates and the purified esterase proteins were studied by immune diffusion, immunoelectrophoresis and enzyme-linked immunosorbent assay (ELISA). InM. persicae, the interactions were specific for E4 and its closely-related mutant form, FE4, and except forPhorodon humuli(Schrank), there was no cross-reaction with homogenates of the nine other aphid species examined. These studies confirmed the quantitative changes in E4 protein previously reported and established that the increased esterase activity inP. humulialso arises from the production of more protein, or proteins, homologous to E4. Resistance ofM. persicaecould be characterized by immunoelectrophoresis even after preservation of the insects in 30% ethanol. Although ELISA could also be used to identify resistance, a simpler immunoplate assay was developed based on measuring the esterase activity of E4 retained when the enzyme bound to IgG. This assay discriminates well between the three resistantM. persicaevariants common in the field in the UK, and its simplicity allows the study of large numbers of insects.