Integrated approach to manage strong resistance to phosphine (PH3) in rusty grain beetle, Cryptolestes ferrugineus

Abstract

Populations of rusty grain beetle, Cryptolestes ferrugineus, a cosmopolitan grain insect pest, have recently developed a very high-level of resistance (1300×) to fumigant phosphine in Australia, threatening the country’s international grain market worth of 8 billion per year. Due to the failure of the registered rates of phosphine, industry urgently needed alternative strategies to manage this new resistance. To address this, an integrated resistance management strategy (IRM) was developed with three core components: 1. regular monitoring and characterization of resistance, 2. developing effective phosphine protocols, and 3. exploring alternative fumigants and treatments. Resistance was monitored across Australia in pest samples collected from farms and centrals storages using a modified FAO method as well as quick knockdown tests. Our results indicated that high-level resistance in C. ferrugineus is prevalent in eastern Australia, particularly in Queensland and New South Wales, particularly in the bulk handing sector. Time to population extinction was assessed in field-derived reference resistant strains using higher dosages (c) and exposure times (t) and the effective c x t regimes were validated in the field for the use by the grain industry. A phosphine concentration of 720 ppm (1 mg L-1) over 18 days was found to be effective in controlling all life stages of phosphine-resistant C. ferrugineus at 25°C. In a parallel research, the suitability of sulfuryl fluoride (ProfumeTM), as an alternative fumigant to phosphine was assessed through laboratory and field efficacy trials. Our results showed that phosphine-resistant insects are highly susceptible to sulfuryl fluoride and a CT of 750 g hm-3 (5.2 mg L-1) over 6 days at 25˚C would be sufficient against all phosphine-resistant pests including C. ferrugineus. While sulfuryl fluoride has promising potential as a “phosphine resistance breaker” the team is currently exploring ways of co-treating phosphine and sulfuryl fluoride, in order to reduce the overall selection pressure against these two fumigants in insects.