In addition to their function in digestion of food, serine proteases (SPs) in insects participate in regulatory cascade pathways in embryonic development and in immune responses (Kanost & Clarke, 2005) . Many haemolymph SPs and serine-protease homologues (SPHs) implicated in immunity contain one or more clip domains at their amino terminus, which may regulate or localize the immune responses stimulated by protease cascades (Jiang & Kanost, 2000) . Among the 57 SP-related proteins in the honey bee genome, 12 SPs and six SPHs contain at least one clip domain, significantly fewer than in Drosophila (24 SPs and 13 SPHs) (Ross et al., 2003) or Anopheles (26 SPs and 15 SPHs), and smaller than the number of clip domain SPs identified to date (n = 14) from expression data in Manduca sexta (Jiang et al., 2005) . Additional phylogenetic and functional relationships among insect SPs and SPHs are discussed in Zou et al. (2006) . Serine protease inhibitors from the serpin superfamily regulate protease cascades in mammals and in arthropods (Reichhart, 2005) . In insect haemolymph, serpins inhibit activated proteases to maintain homeostasis and prevent unregulated activation of immune responses such as melanization or Toll-mediated antimicrobial protein synthesis (Kanost & Clarke, 2005) . In the honey bee genome, there are seven annotated genes encoding five serpins and two proteins with serpin-like regions (GB10078 and GB15070). The number of serpin genes in the honey bee is much lower than in Drosophila (28) or Anopheles (14), mirroring the reduced size of the protease gene family in bees.