This project looked at two aspects of the biology of lesser grain borer, dispersal ability and potential use of food sources other than stored grains.

Research outcomes:

We showed that fluorescent powders are effective for marking beetles used in field studies and that alternating colours are necessary to discriminate between beetles released at weekly intervals, as individuals from previous releases can persist in the local environment for 7-14 days. Recovery of marked beetles from pheromone traps 1 km from the release point was 1.4%, showing this pest has strong dispersal ability over open agricultural landscapes.

Host plant studies showed that lesser grain borers can develop on a range of other plants, however most native plants tested were either unsuitable or very poor hosts. The best alternative hosts were introduced ornamental species. Development of beetles on non-grain hosts takes longer and the adult beetles may also be smaller. So far no lesser grain borers have been recovered from field samples of plants known to support development of this pest in the laboratory.

Research implications:

If further data supports the theory that native plants are unsuitable or very poor hosts for lesser grain borers, and that introduced plant species are being used by lesser grain borers in the field, then there may be a real opportunity to reduce infestation risk in commercial storages through selective management of introduced plant species in the surrounding areas.

The results of this project demonstrate that lesser grain borers have strong dispersal capacity in Australian agricultural landscapes, with close parallels to the situation in the USA. The maximum dispersal distance remains unknown and there would be considerable merit in repeating the work over greater distances and also evaluating dispersal potential across more densely vegetated landscapes. Overseas studies suggest that the maximum dispersal distance for lesser grain borers may be 2-4km. If this holds true, then ensuring that major grain storages have no smaller on-farm storages within 4km would help to mitigate infestation risk, provided alternative food sources in the field are not acting as reservoirs for the beetles.

Acknowledgements:

The authors thank Tom Weir and Rolf Oberpreiler, Australian National Insect Collection, CSIRO, Canberra, for the identification of Coccotrypes carpophagus. Joe Valenzisi, Farm Manager, Yanco Agricultural Institute, and his staff are thanked for working around the large number of insect traps that have been set up all over the Institute. Bernie Dominiak and Laura Jiang, NSW DPI, provided the fluorescent marking powders used in the dispersal studies.