Some aspects of acclimation to low temperatures in the grain weevils Sitophilus oryzae (L.) and S. granarius (L.)

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Abstract
The ability of Sitophilus oryzae (L.) and S. granarius (L.) to acclimate when transferred from 27°C, a near optimal temperature, to 15° C, a marginal temperature, was examined in terms of chill‐coma temperature, dispersal, oxygen consumption and rate of oviposition. The chill‐coma temperature of S. oryzae was higher and the increment of acclimation less than that of S. granarius. Acclimation, although well advanced after 2 weeks after transfer, took more than 4 weeks to complete. Re‐acclimation after the reciprocal transfer took only 2 weeks. The dispersal of S. oryzae held at 15 and 27° C prior to testing differed when the weevils were released in wheat at 27°C but not when released at 15°C. Cold‐acclimated S. granarius dispersed less than warm‐acclimated weevils when released in wheat at both 15 and 27°C. The activity oxygen consumption of cold‐acclimated weevils was less than that of warm‐acclimated weevils. Inverse‐shifts of acutely determined R‐T relationships appeared more significant than changes in temperature sensitivity. Acclimation to 15° C took 8–10 days and re‐acclimation to 27°C about 6–8 days. S. oryzae consumed less oxygen per unit of weight than S. granarius but was more temperature sensitive. Resting oxygen consumption, which was less temperature sensitive than activity consumption, also exhibited inverse acclimation in both species.S. granarius showed evidence of inverse acclimation of oviposition rate after acclimation at 15°C.