Natural Resources Institute, Kent, ME44TB, UK
Many workers throughout India have worked collaboratively in recent years to make important advances in our understanding of the scale and biochemistry of insecticide resistance in Helicoverpa armigera. This paper provides a review of the significance of their work. Mapping of the resistance and its temporal dynamics within and between seasons has been carried out over four years for representative pyrethroids, organophosphates and a cyclodiene. Examination of this data has prompted a number of novel ecological and biochemical studies aimed at elucidating the nature of the changes and the reasons for them. Synergist bioassays and biochemical assays have shown pyrethroid resistance to be mediated through metabolic insensitivity, enhanced circular impermeability, and target site insensitivity. Resistance to organophosphates is through insensitive acetylcholine esterases and enhanced esterases. An esterase dot blot assay has been developed which can be used to rapidly identify resistance mechanisms as well as frequency in large samples. Seasonal shifts in the prevalence of particular mechanisms have now been recorded and in some cases the specific isoenzymes responsible for resistance have been identified. A number of effective synergists have been identified. In addition to standard Integrated Resistance Management (IRM) principles, a number of specific recommendations on the best use of insecticides in common use within India have been generated. These are being incorporated into farmer participatory IRM demonstrations in four states with initial results suggesting that spray costs can be reduced by at least 40% with no reduction in yield in all areas.
