Grain insects

Resistance to phosphine in target pests threatens market access for Australian grain. While the grains industry is now attempting to develop an effective and sustainable strategy to manage this resistance, action is severely limited by significant gaps in our knowledge of the key ecological factors that influence the development of resistance. There is a need to research this information as a foundation for a rational approach to managing phosphine resistance in the Australian grains industry.

Research outcomes:

The project has provided critical research methodologies and preliminary data to fill the large gaps in our knowledge of the ecology of two key pests, Rhyzopertha dominica and Tribolium castaneum, and how this may drive the development of phosphine resistance. This information will contribute to the groundwork for future research needed to provide a scientific basis for a rational resistance management strategy.

Research implications:

The project had a heavy emphasis on field research and the largest effort went to pheromone-trapping programs in two grain growing districts. Trapping showed that beetles of both species were caught across much of the rural landscape especially during the warmer months when grain is harvested and placed into storage. Despite some differences between study areas and species, the results show that infestation pressure is high for a considerable period of the year.

Beetles were trapped near farm silos, in paddocks and in natural vegetation, sometimes 5-10 km from the nearest farm. Unless evidence emerges that these beetles are exploiting resources other than stored grain and grain products, the data suggest considerable movement in the rural landscape. Population genetics analysis of the frozen trap catches may give some insights into movement on a larger scale, but field experimentation is likely to be required to understand movement on a finer scale.

Knowledge of the phosphine resistance status of trapped beetles is essential to understanding resistance development outside of the immediate storage environment, and therefore potential resistance management options. Molecular markers would be best for this purpose but bioassay data from Queensland detected no differences between beetles trapped in paddocks or near silos. 

There are many studies on the survival and reproductive characteristics of R. dominica and T. castaneum under controlled and often ideal conditions, but there is a need to characterise wild beetles of both species. Experiments on individual adults emigrating from infested farm silos showed that most females had mated before emigrating and were capable of reproduction for many weeks without further mating. These results show the colonising potential of these species, and have implications for resistance development.

Growers and other who store grain should take all measures needed to minimise the likelihood of infestations in stored grain bulks, including hygiene, inspecting grain and aeration cooling and chemical control. The project demonstrated heavy infestation pressure from R. dominica and T. castaneum for lengthy periods during the year, and the results to date suggest considerable movement of beetles across the rural landscape. 

Acknowledgements:

We are grateful to the many growers and their families who allowed access to their properties for the research.