CRC50116: Resistance Monitoring

A range of naturalised harmful plant storage pests including beetles, psocids, moths and mites habitually threaten the food safety, market access, trade and the overall profitability and sustainability of the Australian grain industry. Some of these pests have already been detected with resistance to phosphine and the spread of resistance is on the rise annually. In addition, new resistances are also being developed, a recent example being the detection of strong resistance to phosphine in several populations of flat grain beetles. 

There is a need for a robust and systematic national resistance monitoring program to provide both strategic and tactical information on the presence/absence and trends in resistance to phosphine to underpin resistance management in the grain industry and to aid in the identification of factors that affect the risk of resistance in the system.

Research outcomes:

• establishment of a robust sampling protocol to monitor resistance to phosphine and grain protectants in stored grain pests
• standardised national assay methodology for detection of resistance to phosphine
• efficient, effective and comprehensive national data collection and analysis system established using the Australian Grain Insect resistance database.
• established that resistance to phosphine is mediated by the same genes across Australia in major pest species
• established that current impregnated paper assay for resistance to key grain protectants in major storage pests accurately reflects the resistance to respective field application rates
• provided early warning of emergence of strong resistance in rice weevils enabling industry to take timely remedial actions to restrict its development, and 
• diagnosed outbreaks of strong resistance in flat grain beetle providing industry with essential information on which to undertake timely remedial action.

Research implications:

This project has demonstrated that a national resistance monitoring program can contribute significantly to resistance management by providing industry with both strategic and tactical information on the frequency, distribution and strength of resistance.

The information provided by this project emphasises the critical need for industry to adopt the nationally agreed Phosphine resistance management strategy. Our results demonstrate that there is an enormous selection pressure on phosphine. It is imperative that alternatives to phosphine, including other fumigants, be developed to reduce this pressure. An alternative is particularly needed to combat resistance in the flat grain beetle.

Detection of strong resistance in the rice weevil requires that appropriate fumigation protocols be developed to effectively manage this pest and an action plan should be developed to restrict further development of resistance.

Despite the widespread occurrence of weak resistance in the rust-red flour beetle and the saw-toothed grain beetle, strong resistance remains rare in these species. In contrast, strong resistance in the lesser grain borer and flat grain beetle evolved relatively quickly. Future research should also be directed towards investigating the causes and factors that have restricted or promoted the evolution and spread of strong resistance in various species. 

Acknowledgements:

The research team expresses sincere thanks to farmers and the managers and field staff of GrainCorp, CBH and Viterra for their support and cooperation in accessing storage sites for collection of insect samples.