Comparative heat of respiration of five grain beetles in stored wheat

The heat production of five grain beetles in wheat of 14.5% moisture content was measured at two initial grain temperatures of 20 and 30 °C in 10 h using a computer-controlled adiabatic calorimeter. Heat production per individual at both temperatures was highest in Sitophilus granarius (66.1 and 81.4 μW) and lowest in Rhyzopertha dominica (12.5 and 35.3 μW). S. oryzae had the highest heat production rate per unit biomass at 25.3 and 30.6 μW/mg at 20 and 30 °C respectively. Heat production by all species was higher at 30 °C than at 20 °C; the difference was greater for Tribolium castaneum, T. confusum, and R. dominica than for S. granarius and S. oryzae. The rate of heat production by S. granarius at 30 °C decreased with time, the average rate during the first 6 h was 93.7 μW/insect, while during the final 2 h the rate was 58.7 μW/insect. Heat production rates of S. granarius, S. oryzae, and R. dominica increased with time at 20 °C. For all species at both temperatures, the measured heat production was greater than the amount calculated from the respiratory exchange.