Electrophoretic studies on azinphos-methyl resistant and susceptible strains of the lightbrown apple moth, Epiphyas postvittana (Walker) (Lepidoptera: Tortricidae) : A project report presented to the Authority for Advanced Vocational Awards towards a New Zealand Diploma of Science.

Abstract

The literature concerned with mechanisms of organophosphate insecticide resistance and simple monitoring techniques of insects and mites is reviewed. One of the esterase monitoring techniques. The filter paper test, has been found to be very useful in relating esterase levels with toxicological differences in some organophosphate resistant and susceptible insect species.

The development of a quick method using cellulose acetate for studying insect esterases is described. The response of non-specific esterases separated by this technique from Epiphyas postvittana homogenates to a number of substrates and select inhibitors is described. Life stages were compared for their suitability in electrophoretic studies. Six to twelve bands were localised from homogenates of adult abdomens on the electrophoresis strip and their electrophoretic mobilities (Rm) were recorded. Higher non-specific esterase activity and an extra band were found in resistant individuals compared to susceptible strains.

Esterase identification methods were found to be unsatisfactory for resistance studies, especially when inhibition characteristics were used without the confirmation of substrate specificity. This was found to be the case with Epiphyas postvittana also.

A model is used in an attempt to describe the phenotypic (or genetic) make-up of laboratory strains or field samples using the frequency distribution of the total esterase activity.

The possible role of non-specific esterases as a mechanism of organophosphate resistance in Epiphyas postvittana is discussed. Resistance of other insect or mite species to azinphos-methyl and their biochemical relationships are also compared.