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.

What is the biosecurity problem?

Australian export regulations require that all grain exported from Australia is free from insect infestation. This ‘nil tolerance’ standard is also adopted by domestic markets.

The Australian grain industry relies on chemicals, particularly phosphine fumigant, as the key tools used to meet the ‘nil tolerance’ standard. A major drawback, however, with this strategy is the threat of resistance in target species.

A major difficulty for the industry is that there is no practical replacement for phosphine and there are very few contact insecticides suitable for application to stored grain. Faced with this scenario, the industry has no choice but to maintain the tools that it has and must adopt a resistance management strategy to achieve this.

The main outputs of this project are to:

• improve understanding of the factors involved in the development of resistance to phosphine
• validate phosphine resistance management tactics
• improve understanding of distribution of species of flat grain beetle species and the role of gene flow in selection for resistance to phosphine 
• validate molecular resistance diagnostic tools and analysis of resistance gene frequencies.  

Who will be the end-users of this research?

The primary end-users will be:

• grain companies, farmers and other grain storers. In particular, individuals with responsibility for managing grain biosecurity
• officers with responsibility for biosecurity research and policy within government and non-government organisations.

Flat grain beetle (FGB) is a major emergency plant pest (EPP) of stored grain in Australia. Populations of FGB have recently developed high level resistance to phosphine (the only viable fumigant available for non-quarantine use) resulting in control failures with current dosage regimes.

As there is no practical alternative to phosphine, failure to control FGB with phosphine places at risk market access for Australian grain worth up to $7 billion in annual trade. Therefore there is an urgent need to develop appropriate phosphine fumigation protocols to eradicate outbreaks of strongly resistant FGB.

Research outcomes:

• Characterisation of high resistance to phosphine in flat grain beetles (FGB) for the first time internationally.
• Establishment of fumigation protocols and an eradication strategy that will enable industry to eradicate infestations of phosphine-resistant flat grain beetle and prevent or delay further selection for resistance to phosphine.
• Development of a rapid test to detect highly resistant FGB.
• Facilitate continued market access of Australian grain.

Research implications:

The success of Australia’s $7 billion grain industry depends on the maintenance of high standard in its post-harvest produce through effective pest management. The absence of detectable levels of insect infestation is such an important issue to world grain markets that to maintain its competitiveness in premium markets, Australia guarantees supply of an insect-free product. This strategy is enforced by Australian Quarantine and Inspection Service (AQIS) through the Exports (Grain) Regulation that specifies a ‘nil tolerance for live insects’ on all grain leaving the country. Nil tolerance for live insects is also the standard generally adopted by domestic buyers of grain.

The most cost-effective method to meet the Exports (Grain) Regulation is the application of chemicals to grain. Currently, the industry relies on a single fumigant, phosphine, because of an increasing sensitivity of grain markets to the presence of pesticide residues, the development of insecticide resistance to other chemical alternatives and the lack of practical alternatives. Phosphine has the enviable reputation for being relatively cheap, accepted as a residue-free treatment internationally and having flexibility in its application. Traditionally, the grain industry has managed resistance essentially by replacing redundant chemicals with new materials. Chemical treatments are favoured because available non-chemical methods, on the whole, are either significantly more expensive, less versatile, do not easily match grain-handling logistics, are less effective or require significant capital investment. Therefore, the chemical replacement strategy is no longer viable and at least for the medium term, the Australian grain industry will need to rely on phosphine for disinfestations of its stored commodities to meet the market demands.

The CRCNPB-supported FGB fumigation protocol development project has delivered two new fumigation protocols that can control highly resistant FGB populations. In addition, an eradication strategy has now been deployed that will eradicate infestations of phosphine-resistant FGB and prevent or delay further selection for resistance to phosphine and restrict their spread.

A direct implication of the research finding is that by extending the life of the effective use of phosphine, industry will avoid the use of contact pesticides for the time being. This will in turn avoid potential trade issues and save the industry from significant economic loss.

An independent cost-benefit analysis for this project by GRDC (Ross McLeod) has suggested that even if there are significant changes to key variables such as costs of fumigation, probability of success and volumes of grain treated with contact insecticide, prolonging the life of phosphine through development of new protocols will still result in substantial economic benefits.

Acknowledgements:

The research team expresses sincere thanks to farmers and the managers and field staff of GrainCorp, CBH and Viterra for their support and help for accessing storage sites for collection of insect samples and undertaking field trials. The team would also like to thank GRDC for their support throughout the research.

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.

Outcome

Response: Reduced losses from incursions by harmful pests and diseases.

Goal

Reduced economic and social impact from incursions of harmful pests and diseases through new control, risk mitigation and recovery strategies.

Indicators of success

Economic:

Decreased economic and social cost for future pest and disease eradications and scientific defensibility of market access conditions.

Science:

New tools to optimise incursion responses accepted by peers through scientific publication and invitations to present at key meetings, conferences and workshops.

Policy:  

New tools to manage plant biosecurity threats are integrated into response strategies through consultation with end-users.

Impact/Adoption: 

New procedures for the eradication of plant biosecurity threats are used by end-users.