There is considerable interest in the continued development of sustainable population management protocols for Megachile rotundata (F.) (Hymenoptera: Megachilidae), an adventive, gregarious, cavity-nesting, leafcutting bee that has been extensively cultured throughout North America as a superior pollinator of alfalfa (Medicago sativa L.). In an effort to clarify the timing of the prepupal diapause to post-diapause (cold-mediated quiescence) transition in M. rotundata, we studied differential gene expression and respiration at selected, biologically-relevant intervals throughout its diapause and post-diapause program. We employed constant volume respirometry to measure oxygen consumed and carbon dioxide produced, as an indicator of overall metabolic activity. Partial clones for five selected genes including two from the 70 kDa and one from the 90 kDa stress protein families were developed via RT-PCR, and Northern blotting was used to compare gene expression in a population held under natural conditions from December 2002 to June 2003. We detected differences in expression patterns of individual genes prior to detecting differences in respiration levels, suggesting that the actual prepupal diapause to post-diapause (cold-mediated quiescence) transition in M. rotundata occurs far earlier that previously thought. Our results also appear to be consistent with the hypothesis of cascading changes in thermal responses proposed to explain diapause development in the egg of gypsy moth (Sawyer et al., Ecological Modelling, 66:121-155, 1993), where no clear demarcation is assumed between diapause and post-diapause development and initial developmental responses having low thresholds and optimal temperatures gradually give way to responses having higher thresholds and optima.
Species 1: Hymenoptera Megachilidae Megachile rotundata (alfalfa leafcutting bee)
Keywords: heat shock proteins, actin
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