The JAK/STAT signalling pathway may also contribute to innate immunity by induction of complement-like factors and the overproliferation of haemocytes. JAK/STAT appears to be initiated via cytokine-like molecules in blood cells (Agaisse & Perrimon, 2004) . In flies, the extracellular glycosylated protein Upd acts as a ligand that activates the JAK/STAT pathway, which in turn promotes phagocytic activity of haemocytes. The JAK/STAT pathway has also recently been shown to participate in an antiviral response in Drosophila (Dostert et al ., 2005) . Honey bee homologues for the Drosophila JAK/STAT signalling pathway (Fig. 2 ) comprise the cytokine receptor domeless (Dom), JAK tyrosine kinase (Hopscotch), the STAT92E transcription factor 3. Transcript abundances for immune candidate genes in adult workers 24 h after injections of Escherichia coli (Ec), saline buffer, or the bee pathogen Paenibacillus larvae , and controls (left four columns). Two columns on right show transcript abundances in 2nd-instar larvae challenged orally with an infective dose of P. larvae or unchallenged controls. Cluster A = genes strongly up-regulated by adult injection or wounding, Cluster B = genes up-regulated in infected larvae, Cluster C = genes down-regulated or minimally changed in challenged bees. and two negative pathway regulators SOCS (suppressor of cytokine signalling) and PIAS (protein inhibitor of activated STAT). Orthologues of two recently identified components of this pathway (Baeg et al ., 2005; Muller et al ., 2005) , the tyrosine phosphatase Ptp61F (XP392429) and the WD40and bromo-domain-containing protein BRWD3 (XP395263), are also present in the honey bee. Although the key ligand (Upd) for the JAK/STAT pathway was not found in the honey bee genome, the presence of the gp130 cytokine receptor homologue Domeless and all other members of the signalling pathway indicates that this mechanism may be common across insects and is intact in honey bees as well as in flies. In addition to up-regulating the complement-like thiolestercontaining proteins (TEPs; Lagueux et al. , 2000; Boutros et al ., 2002) , the JAK/STAT pathway in Drosophila regulates expression of the Turandot (Tot) genes that encode humoral factors induced by severe stress Agaisse et al ., 2003) . None of the Tot factors (Tot A-Z) are apparent in honey bees.