A two-step approach to monitoring changes in susceptibility to sulfuryl fluoride in red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) and its implication for the industry

Abstract

Sulfuryl fluoride (SF) is an inorganic fumigant, currently being used widely to disinfest various postharvest commodities and processed products. Though SF has been used in treating stored commodities for more than two decades, so far, no information is available in relation to monitoring the changes in susceptibility levels to SF in stored product insects. In this study, we characterized dose mortality responses to SF in multiple field insect populations and phosphine-resistant reference strains of red flour beetle, Tribolium castaneum, towards establishing a discriminating dose for detection of resistance. Adult beetles, after two weeks of eclosion, were exposed to a series of SF concentrations (0.05–2.5 mg L−1) over 48 h (2.4–120 g hm−3). Mortality response in each population/strain was evaluated after 7 days and subjected to probit analysis. A two-step approach was adopted, both based on the key toxicity parameters, LC values, response ratio, and confidence intervals. Firstly, LC95 of the most susceptible population, 0.84 mg L−1 over 48 h (40 g hm−3) was identified as the baseline dose and proposed to monitor changes in susceptibility levels to SF in freshly collected field populations of T. castaneum. Then the discriminating dose was derived, 1.7 mg L−1 over 48 h by multiplying LC95 of the most susceptible population by a factor of 2, which could potentially be used to identify genetically resistant individuals to SF. Dose mortality responses of T. castaneum populations/strains from Australia revealed low-level (1.8-fold) region-wide variations in basal tolerance to SF, emphasizing the importance of adopting a two-dose approach to monitor resistance to SF. Overall, our results hold enormous potential for researchers and stakeholders in Australia and across the globe towards its use in the early detection of resistance to SF in T. castaneum and its management.