Integrated pest control strategy for stored grain

Abstract

A storage strategy, based on reducing grain temperatures by ambient aeration, has been devised and tested in large-scale trials. Twenty-tonne lots of wheat, with an initial moisture content and temperature of between 12.5 - 16.5% and 27 - 35°C, were stored in a nest of metal bins. An infestation of Oryzaephilus surinamensis (saw-toothed grain beetle), Sitophilus granarius (grain weevil) and Cryptolestes ferrugineus (flat (red-rust) grain beetle) was introduced into the grain at the rate of 1, 1 and 0.4 insects/kg of grain respectively.

During storage the grain was cooled by means of ambient aeration, with air blown up though the grain at the rate of 10 cu. m./tonne/hour. The bins were divided into two batches of three and the aeration system of each batch was controlled separately by a differential thermostat. In one case a differential of 2°C was used but a differential of 4°C was used for the other controller. The effects of time and changes in temperature on the insects were monitored by a combination of trapping and spear sampling. Aeration produced a rapid fall in the temperature of the grain so that the grain at the centre of all bins was below 15°C five days after the start of cooling. Ten weeks after the start of aeration grain temperatures were near or below 5°C. There was a marked difference between the number of hours of fan operation used by the two differential settings to achieve the same grain temperatures. The 4°C differential used only about a third of the hours of the 2°C setting. Numbers of 0. surinamensis and C. ferrugineus caught at the surface increased at the start of aeration but, as the trialprogressed, declined to a very low level. Spear sampling 24 weeks after cooling began, showed that the insect population had fallen from about 2.4/kg to less than l/kg. When the grain was sampled during out-loading at the end of the trial, no live insects were detected.

Data to validate the results from practical trials has been generated by calculation or by field observations. These show that the strategy is not susceptible to climatic and geographic variations and would be successful throughout the U.K. in any year. Minimum rates of airflow and the consequences in terms of rate of cooling and insectinfestation of not achieving these airflow rates have also been calculated. Field observations have confirmed that the method of monitoring insect population developed for the strategy is effective and likely to be more sensitive at low population densities than spear sampling.

Aeration records and trapping data have been collected from a range of commercial stores. These confirm the effectiveness of trapping and have allowed the costs of aeration under commercial conditions, to be estimated.

Limited applications of pesticide to bulks of cooled grain were shown to be effective under practical conditions. They were also much less expensive than alternative chemical control options and resulted in a large reduction in pesticide usage.

Further work on the integrated storage strategy is reported as Project Report No 57.