Development and characterization of expressed sequence tags from the alfalfa leafcutting bee (Megachile rotundata)

Alfalfa leafcutting bees, Megachile rotundata (Fabricius), are extensively used in western North America to pollinate alfalfa for seed production. However, the larvae are commonly infected by fungi in the genus Ascosphaera, the cause of chalkbrood. To uncover mechanisms associated with disease development and bee immune response, we constructed cDNA libraries from early forth instar larvae of healthy and infected bees by using the SMART cDNA library kit. Approximately 2,070 valid ESTs were generated to form 199 contigs and 680 singletons, with a total of 879 putative transcripts. The initial analysis of our dataset found that the majority of ESTs have putative functions associated with metabolism and protein synthesis. However, we have also found ESTs encoding for heat shock protein, CuZn superoxide dismutase, thioredoxin, hexamerins, ferritin, extensin, and cellular retinaldehyde-binding protein, all of which may be involved in host immune responses, as identified in other organisms. Further comparisons will be postured, including comparisons with the honey bee genome and between the libraries we generated for healthy versus infected M. rotundata.