The effect of thermal acclimation and relative humidity on the oxygen consumption of three Sitophilus species

The oxygen consumption of adult Sitophilus oryzae (L.). S. granarius (L.) and S. zeamais Motsch, that were acclimated at 27 or 15°C was measured at constant temperatures of from 10 to 30°C and relative humidities of 94, 70 or 50%. Warm-acclimated weevils that were free to move within the respirometers used significantly more oxygen than cold-acclimated weevils in almost all measurement regimens. In general, oxygen uptake was greatest at 70% r.h., intermediate at 94% and lowest at 50%. High oxygen consumption in certain regimens suggested an interaction between the effects of humidity and measurement temperature in S. oryzae and, to a lesser extent, in S. granarius. An interaction between humidity and acclimation temperature was indicated in S. granarius by the finding that the Q₁₀s of warm-acclimated weevils increased as humidity decreased whereas the Q₁₀s of cold-acclimated weevils did not change. The relationships between the logarithm of oxygen consumption and measurement temperature were described in all three species by quadratic functions. The oxygen consumption of S. oryzae closely restrained within the respirometers was not affected by relative humidity. Such weevils consumed more oxygen at 15 and 20°C when warm-acclimated than they did when cold-acclimated; there was no significant difference, however, between the oxygen consumption of warm- and cold-acclimated weevils at either 25 or 30°C.