Examining the gene expression differences underlying social development and behavior has been termed sociogenomics . Sociogenomics is predicated on two observations: "social life has a biological basis and thereby is influenced by genes and evolution" and "molecular functions of many genes are conserved across species" . Therefore, it is possible to examine eusocial species such as termites, honey bees, ants, and social wasps in an ecological and molecular context to better understand the genetics, function, and origins of eusocial behavior.
Termites (Isoptera) are a large and diverse group of eusocial insects. Although eusociality is believed to have evolved only once in Isoptera, the ~2600 described species show enormous diversity in life history, behavior, colony composition, morphology, physiology, ecology, and biogeography [2, 3]. Members of the genus Reticulitermes (Rhinotermitidae) are found throughout much of the contiguous United States, with introduced populations in Europe, South America, and the Bahamas . Reticulitermes flavipes Kollar, the eastern subterranean termite, is the most common species in the United States. R. flavipes colonies, like those of other termites, consist of morphologically and behaviorally specialized castes. All individuals emerge from eggs as larvae, beyond which the development is flexible in that larvae may develop into nymphs and subsequently into dispersing alates, or into the sterile workers or soldiers [reviewed in ref. ]. Workers are involved in nest building, tunnel maintenance, and brood care whereas soldiers defend the colony and possibly communicate general colony fitness. Workers and nymphs of R. flavipes may develop into supplementary reproductives under certain conditions [2, 3].
Historically, Reticulitermes spp. have been difficult to study mainly due to their cryptic living conditions and amorphous nest structure [2, 5]. However, the advent of genomic and bioinformatic methods has provided new opportunities to study these organisms . A macroarray study of R. flavipes  demonstrated differences in gene expression among the different castes. Genes that exhibited differential expression between workers and soldiers included salivary cellulases, endoglucanases, tubulins, and troponins .
Other examples of differential gene expression among termite castes include higher expression of the mitochondrial cytochrome oxidase-III subunit in workers and nymphs of R. santonesis , increased cytochrome P450 levels after methoprene application in soldier and pre-soldier fat body in Hodotermopsis sjostedti and Nasutitermes takasagoensis [8, 9], and a gene specifically expressed in H. japonica soldier mandibles termed SOL1 thought to be involved in soldier specific behavior .
In the well-studied eusocial honey bee, Apis mellifera, there is a tendency for behaviorally associated genes to exhibit a G+C bias within promoter regions when compared to Drosophila melanogaster and more cis -regulatory elements  as well as high levels of expression of ribosomal and hexameric storage proteins in queen and worker cDNA libraries . An EST analysis revealed that honey bee workers showed an over-expression of genes involved in cell differentiation and hydrolase activity, whereas honey bee queens exhibited an upregulation of genes involved in metabolism and oxidoreductase activity .
Given that there has been no large-scale effort to identify expressed genes in termites, our first objective was to characterize R. flavipes genes by analyzing an EST database of ~15,000 clones from three cDNA libraries constructed from workers, soldiers, and alates as well as two cDNA libraries constructed from early and late termite larval stages. Our second objective was to undertake an in silico analysis of expression patterns among the castes and life stages to tentatively identify putatively differentially expressed genes.