Ecology of Sitophilus and Cryptolestes species
Project Type & Status
Impact Delivery Themes
Ecology of Sitophilus and Cryptolestes species
Final Report Summary
The aim of this project was to investigate the ecology of Sitophilus and Cryptolestes species in all three grain-growing regions of Australia as well as in Kansas, USA, and to integrate the knowledge generated into strategies for the management of these insect pests of stored grain.
Research questions included:
are these pests limited to the storage environment
how far do pests disperse on local and national scales
how quickly do pests reinfest stored grain, and
does carrying phosphine resistance alleles affect ecological fitness and therefore the development of resistance?
The project also included studies on the potential for using network modelling to predict grain insect and resistance spread across regions, and optimise sampling strategies; and Near Infra-Red Spectroscopy (NIRS) for distinguishing morphologically similar Cryptolestes species.
The results of this project have provided insights into the ecology of two major pest species, S. oryzae and C. ferrugineus, which in turn provide a basis for recommendations to industry. The project has also evaluated or delivered new tools for future use by industry or researchers.
There was little evidence of flight dispersal in S. oryzae highlighting the importance of within-farm and within-depot sources of infestation. In contrast, there was strong evidence of flight dispersal in C. ferrugineus. There was strong seasonality in flight activity of C. ferrugineus probably linked to seasonal changes in ambient temperature. Both species were capable of infesting experimental grain bulks located near farm silos, especially when nearby silos were already infested. Only C. ferrugineus was capable of infested experimental grain bulks located 2 kilometres away from farm silos.
In the case of C. ferrugineus, there is considerable gene flow occurring on a regional scale in Australia, but gene flow between the west and the east is restricted. In contrast, the results for S. oryzae show a more ‘patchy’ distribution supporting the view of limited flight dispersal in this species. The gene flow results show the potential for movement of beetles and resistance genes within and between regions. Movement of infested grain by humans must be contributing to this through movement of insects in grain and harvesters and other machinery.
There was no evidence that being strongly phosphine resistant comes at a cost. This suggests that strong resistance will persist in populations where it has been selected for through inappropriate fumigation.
The project evaluated or delivered several new tools. There are several morphologically similar Cryptolestes species. The project confirmed that a published molecular tool was effective for use on Australian population samples to distinguish between the more economically important C. ferrugineus and other pest species. The project also showed that Near Infrared Spectroscopy has potential for this purpose, but requires more validation.
The project has delivered new population genetic tools in the form of microsatellite markers for S. oryzae and C. ferrugineus. Potential was clearly demonstrated for using network modelling to predict grain pest and resistance spread across regions, and optimise sampling strategies was investigated. A new commercial pheromone lure for C. ferrugineus was evaluated in the laboratory and field. The lure has potential for research and practical applications.
Knowledge of the ecology of the stored grain pests, Sitophilus and Cryptolestes spp., and resulting strategies will contribute to the continuation of Australia’s reputation for high quality and insect-free grain. Two species in particular, C. ferrugineus and S. oryzae, warrant attention because the development of strong resistance to phosphine threatens this reputation. Farm hygiene recommendations include:
With flight activity being linked to seasonal changes in ambient temperature it follows that farmers and others who store grain should not delay hygiene practices until close to the wheat harvest (spring-summer), but undertake them well before flight increases in spring.
Grain bulks were more likely to be infested on farms when infested grain was already present. This shows that farmers and others who store grain need to monitor their silos for insect infestations and to eliminate them when they occur.
There may be no safe distance from farm silos to dump waste grain. Although the risk of infestation from waste grain will be reduced with distance, the safest option is to bury or burn the waste grain to reduce the risk to nil.