Managing evolving insecticide resistance in stored grain pests within Avon Region, Western Australia

Abstract

The requirement that all Australian grain exports are insect-free relies on phosphine fumigation to control stored grain pests such as the lesser grain borer (Rhyzopertha dominica).The value of the current infrastructure in the grain storage, transport and handling network depends on the efficacy of phosphine fumigation. However, the biosecurity of the grain supply network is threatened by the emergence of Strong-Form Resistance (SFR) to phosphine in stored grain pests. SFR spreads from farm to farm through dispersion and by transport with grain through the supply network. The presence of SFR increases costs in the supply network as the number of fumigations per grain batch increases and the requirement to hold grain in sealed storage to achieve effective pest control increases. SFR in the short run increases costs of phosphine fumigation. In the long term it requires additional investment in sealed storage. This paper analyses the additional costs of SFR in the Western Australian Avon Region using three linked economic and bioeconomic models. Model 1 (farm to receival site) maximizes farmer’s profit of delivering wheat from farms to receival sites. Model 2 (recieval site to port) minimizes the Co-operative Bulk Handler’s (CBH) costs of transport, handling, storage and fumigation costs from receival sites to port. Model 3 (biosecurity – resistance spread) calculates the expected extra biosecurity cost of emerging SFR for the Avon wheat network. Our results show an increase in costs of between $8.8/t to $31.4/t of wheat depending on the rate of spread and the time horizon considered. Key words: Phosphine fumigation, biosecurity, crop storage, wheat, stored-wheat outbreak, jump diffusion.