This week in Genome Biology, researchers describe their extensive annotation of the immune and stress gene repertoire of Acyrthosiphon pisum, the pea aphid, whose genome was sequenced and reported in PLoS Biology this week. Nicole Gerardo of Emory University and her colleagues write that they were surprised to find that pea aphids appear to be missing genes present in other insect genomes which appear to be critical for recognizing, signaling, and killing microbes.