Influence of thermal acclimation on the survival of Sitophilus granarius (L) and Oryzaephilus surinamensis (L) at low temperatures

Low temperatures have been used for many years to control populations of stored-product insects. The aim of aeration was primarily to cool down the grain and then to prevent its deterioration by reducing the number of insects. In Belgium, the mild winters enable insects to survive to the next season. In autumn, the progressive lowering of temperature has an acclimation effect on stored-product insects. The present study was undertaken to determine the survival at low temperatures of non cold-acclimated and laboratory- and field-cold-acclimated insects. We have chosen to work with the granary weevil Sitophilus granarius (L.) and the saw-toothed grain beetle Oryzaephilus surinamensis (L.). They are the most frequent stored-grain pests in Belgium. To compare the cold-hardiness of different laboratory cold-acclimated insects, S. granarius and O. surinamensis were placed at nine different cold-acclimation temperature regimes. Insects were kept at 5 degrees C for 2, 4 and 6 weeks or at -5 degrees C for 4, 7 and 14 days. To assess the field-cold-acclimation in autumn and in winter, insects were monthly taken from a bin and transferred to 5 degrees C for 6 weeks. S. granarius adults were more cold-hardy than O. surinamensis, but O. surinamensis adults compensated their cold-sensibility by a great ability to acclimate. S. granarius is able to survive the winter in Belgium because of its cold-hardiness while O. surinamensis survives because of its ability to acclimate to low temperatures.