The effects of grain cleaning on the development of Sitophilus oryzae infestation

Abstract: It is known that grain cleaning makes it possible to fight against secondary pests. Indeed, at the same time as impurities are removed, aspiration and screening of the cleaner are helpful to remove insects from grain. However, immature stages of primary pests like Sitophilus oryzae hide inside kernels so they cannot be separated from the grain this way. Previous studies have shown that mechanical disturbance of infested grain may prevent immature stages from developing successfully, especially when the physical stress is carried out regularly.That is why we have studied the effects of grain cleaning on S. oryzae depending on the cleaning frequency applied during an 8-week treatment. We have monitored adult densities in mini storage silos filled with 290 kg of infested soft wheat and cleaned once every two weeks, once or twice a week, three times a week or never cleaned. A regular sampling has also been done and grain samples have been incubated during 6 weeks in order to measure the emergence rate in each silo.The results demonstrate that a grain cleaning carried out twice or three times a week prevents a dramatic growth of adult beetles in the silo and it reduces emergence of S. oryzae by more than 90%. One cleaning per week shows an intermediary efficacy with a 70% decrease of emergence compared to uncleaned silos. Only one cleaning every two weeks nevertheless seems insufficient to control pest development under the ambient conditions of this study that were favourable for insects.