Cyclic CO(2) emissions during the high temperature pulse of fluctuating thermal regime in eye-pigmented pupae of Megachile rotundata.

Megachile rotundata (Hymenoptera: Megachilidae), the primary pollinator used in alfalfa seed production, may need to be exposed to low-temperature storage to slow the insects' development to better match spring emergence with the alfalfa bloom. It has been demonstrated that using a fluctuating thermal regime (FTR) improves the tolerance of pupae to low temperatures. Carbon dioxide emission rates were compared between four different FTRs, all with a base temperature of 6°C and a daily high-temperature pulse. Four different high-temperature pulses were examined, 15 or 25°C for 2h and 20°C for 1 or 2h. A subset of pupae at the FTR base temperature of 6°C exhibited continuous gas exchange and, once ramped to 20 or 25°C, shifted to cyclic gas exchange. As temperatures were ramped down from the high-temperature pulse to 6°C, the pupae reverted to continuous gas exchange. The following conclusions about the effect of FTR on the CO(2) emissions of M. rotundata pupae exposed to low-temperature storage during the spring incubation were reached: 1) the high temperature component of the FTR was the best predictor of respiratory pattern; 2) neither pupal body mass nor days in FTR significantly affected which respiratory pattern was expressed during FTRs; 3) cyclic gas exchange was induced only in pupae exposed to temperatures greater than 15°C during the FTR high temperature pulse; and 4) a two hour pulse at 25°C doubled the number of CO(2) peaks observed during the FTR pulse as compared to a two hour pulse at 20°C.