Effect of vacuum storage of wheat (Triticum aestivum) grain on the granary weevil, Sitophilus granarius and wheat quality

In laboratory experiments, 30 adults of the granary weevil, Sitophilus granarius (L.) were transferred onto 1.3 kg wheat (Triticum aestivum L.) grain in open 2 l vacuum bags. The grain had an initial m.c. of 9.5, 12.5, 14.0 and 15.5%. Beetles were allowed to feed and oviposit for 7 days before drawing a vacuum in the vacuum bags used for this purpose. The vacuum aimed for was 50%, reducing the ambient oxygen content from 20.9% to about 10.5%. For each tested parameter, three bags were flushed with nitrogen to restore ambient pressure and again vacuumed once, twice or three times to further reduce the initial oxygen content to 5.3, 2.6 and 1.3% respectively. Bags were subsequently stored at 20°C for 3, 6 , 12 or 24 months. Only one beetle was found to have survived three months of storage and no survivors were found after longer storage periods. Grain quality was not affected by the presence of weevils nor the initial residual oxygen content, while initial moisture content had a marked effect. It is therefore possible that the reduced pressure and resulting oxygen content interfered with insect movement, feeding, and respiration. Vacuum storage in flexible bags could be a suitable method for pest prevention of sufficiently dry stored products even if a moderate infestation had already occurred.