Chill-coma and Minimum Movement Temperatures of Stored-Product Beetles in Stored Wheat

The minimum temperature at which stored-product insects can move inside stored grain bulks with different grain moisture contents is not known. The movement of adults of four stored-product insects, Cryptolestes ferrugineus (Stephens), Tribolium castaneum (Herbst), Sitophilus oryzae (L.), and Sitophilus zeamais (Motschulsky), at low temperatures inside jars or bulks of wheat with 11.1 or 16.0% moisture content was measured. Spontaneous walking stops (SMh), CCT (no movement after shaken), and minimum movement (TMmin, caught in probe pitfall traps) temperatures were determined at stepped-decrease of temperature. The ranges of SMh, CCT, and TMmin temperatures of the four stored-products beetles were 4.0 to 9.0°C, 2.0 to 8.0°C, and 6.0 to 11.5°C, respectively. The TMmin was ∼3°C higher than the SMh for all the tested beetles. C. ferrugineus had the lowest SMh, CCT, and TMmin temperatures, whereas S. zeamais had the highest values of these determined temperatures. C. ferrugineus under a faster stepped-decrease of temperature had higher SMh, CCT, and TMmin temperatures than that under a slower stepped-decrease of temperature, while adults of T. castaneum were not influenced by the temperature decrease rate. The two species of Sitophilus did not survive to the end of the experiment at the faster stepped-decrease of temperature. Two grain moisture contents did not affect these determined temperatures for all tested species.