Mechanisms of phosphine toxicity and resistance

Phosphine resistance is a serious developing problem for food security worldwide, especially for stored grains. The Australian grains industry especially is heavily reliant on this fumigant to maintain insect-free grain. In order to enhance resistance management strategies, we have aimed to identify the genes responsible for resistance in order develop genetic markers, so that rapid testing of field collected insects can be performed.

We have used genetic linkage and next-generation genomic sequencing approaches to identify the genes responsible for phosphine resistance in the pest insects Tribolium castaneum (Rust Red Flour Beetle) and Rhyzopertha dominica (Lesser Grain Borer). To date, we have found through genetic studies that high-level resistance is conferred by two loci, rph1 and rph2 that have synergistic interactions.

We have also found through genetic complementation studies that these resistance loci are highly conserved within species. We have identified one gene at the rph2 locus, responsible for high-level resistance in both T. castaneum and R. dominica, demonstrating that resistance is also well conserved between species. Sequencing of the mutations that confer resistance in this gene from multiple high-level resistant strains has highlighted the probable mechanism for phosphine mode of action as well as mechanisms for resistance. The biological effect of the phosphine mode of action has strong implications for redox biology and also fumigant chemistry.