Temporal variation in overwintering gene expression and respiration in the solitary bee Megachile rotundata

Abstract

Partial clones of Megachile rotundata HSP90, HSP70, HSC70 and actin were developed by RT-PCR. These clones were used to generate probes to screen for the expression of their respective transcripts in heat-shocked pupae and in diapausing prepupae through post-diapausing pupae. Northern blot analysis revealed transcript sizes for MrHSP90, MrHSP70, MrHSC70, and Mractin of 3.6, 2.3, 2.5, and 1.4 kb, respectively. MrHSP90 and MrHSP70 were highly upregulated in post-diapausing pupae exposed to 40 °C for 1 h, while MrHSC70 was only slightly induced by heat shock. Levels of MrHSC70 and MrHSP90 showed little change between field collected diapausing prepupae and post-diapausing pupae. In contrast, MrHSP70 was highly upregulated in diapausing prepupae and Mractin was at or below the level of detection in diapausing prepupae. Transferring field reared overwintering prepupae in February to 25 °C for 3 days induced an expression pattern of MrHSP70 and Mractin more typical of post-diapausing bees, indicating the likelihood that the transition to post-diapause development had occurred prior to February. However, measurements revealed possible cyclic respiration patterns, including low respiratory quotient (RQ) values during February and March and a transition during April to more continuous respiration with elevated RQ values.