Lowering the moisture content of stored grain can gain extra time for cooling to prevent infestation: studies on the development, productivity and survival at two relative humidities of two insect species on whole wheat and an artificial diet

摘要

Details of insect biology are directly linked to recommendations for control. For instance, the time available to cool and hence engineering design, depend on speed of development. However, past work has concentrated on the biology on ideal diets and not on grain. Comparison of the development times of recently collected UK strains of the saw-toothed grain beetle, Oryzaephilus surinamensis, and the rust-red grain beetle, Cryptolestes ferrugineus, indicates that development is extended on whole grain compared with that on the usually employed laboratory diet. The current recommendation for passing a cooling front through grain for insect control, based on past work using a laboratory diet and tropical strain, can probably be safely extended from two weeks to three weeks, as the quickest observed development on wheat was 19 days. Furthermore, reducing relative humidity (r.h.) from 70 to 50 percent (15-12 percent m.c.) dramatically reduced the proportion able to complete development on wheat, whileit had little effect when a laboratory diet was used. Should the speed of cooling become problematical due to climate change, moisture reductions may extend the cooling time available. There was little difference at 5 deg C between the survival of O. surinamensis on wheat or artificial diet, but at 10 deg C, they survived for a shorter time on whole grain, presumably because they still needed to feed above chill coma temperatures. If temperatures below 10 deg C become difficult to achieve, moisture reductions may assist low temperature disinfestation. Productivity on a laboratory diet was enhanced by over 10x compared with that on wheat, and while humidity had no effect on a laboratory diet, it effectively increased the lower temperature-breeding threshold on wheat. Previous estimates of time to exceed detection threshold based on reproduction rates on substrates other than whole grain have therefore been unrealistic.