Decision analysis of insecticide resistance in light-brown apple moth

Light-brown apple moth (Epiphyas postvittana) has developed a low level of resistance to azinphos-methyl in two small areas of a major horticultural district in New Zealand. It is not known whether resistant individuals form isolated populations or are a part of a much larger population. Hence, it is uncertain whether this resistance has the potential to develop and spread. Models representing the range of possible situations are described and management options assessed by deducing the consequence they would have in each of the possible situations. It is concluded that the continued use of organophosphate insecticides incurs the risk of a development and spread of resistance. The best alternative is to use pyrethroids in the affected areas but such an option is not without its own costs.