Submitted to: Genbank
Publication Type: Other
Publication Acceptance Date: September 30, 2002
Publication Date: April 29, 2004
Citation: Yocum, G.D., Kemp, W.P. 2004. Diapause regulated gene expression and respiration in field collected overwintering alfalfa leafcutting bees, Megachile rotundata. Genbank. Accession nos. AY550115-AY550118. Technical Abstract: Megachile rotundata is a cavity-nesting, leaf-cutting bee that has been extensively cultured as a superior pollinator of alfalfa, following the first North American records of its presence. At present, M. rotundata is the pollinator of choice for alfalfa seed production on more than 70,000 ha in western North America, and is the most widely used commercially managed pollinator, after the honey bee, Apis mellifera L. M. rotundata overwinter as diapausing prepupae. Knowledge about diapause physiology is needed in order to decrease mortality during overwintering storage and to more accurately time diapause termination with early spring bloom of targeted crops. Investigations were undertaken to determine if the expression levels of selected mRNA transcripts, 70 and 90 kDa heat shock protein families and actin, could provide us with a better understanding of the sequential aspects of diapause development in M. rotundata prepupae under field conditions beyond that provided by constant volume respirometry. Levels of MrHSC70 and MrHSP90 showed little change between field collected diapausing prepupae and nondiapausing 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 25oC for 3 days induced an expression pattern of MrHSP70 and Mractin more typical of nondiapause bees, indicating that true diapause terminated before February. However, respiration measurements revealed possible diapause respiration patterns from January through March, transitioning during April to nondiapausing respiration patterns. The results of this investigation lead to the development of the following hypothesis: There are at least two subsets of genes expressed in overwintering temperate zone insects. The first subset regulates true diapause development, with true diapause being defined as the inability of the insect to respond to favorable environmental cues for subsequent development. The second subset consists of the overwintering genes that enable the insect to survive extreme environmental conditions encountered during winter.