In insects, chitinases play an essential role in the degradation of old exoskeleton and turnover of the gut lining. In silico screening of the entire genome of the pea aphid (Hemimetabola), Acyrthosiphon pisum, detected nine genes encoding putative chitinase-like proteins, including six enzymatically active chitinases, one imaginal disc growth factor, and one endo-beta-N-acetylglucosaminidase. Screening of the genomes of Aedes aegypti, Anopheles gambiae, Apis mellifera, Bombyx mori, Culex quinquefasciatus, Drosophila melanogaster, Nasonia vitripennis, Pediculus humanus corporis, and Tribolium castaneum suggested repeated gene duplications in holometabolous lineages. Quantitative reverse transcription-PCR demonstrated the expression of four and two distinct chitinase-like genes of A. pisum to be highly up-regulated in the embryo and the midgut, respectively, suggesting specific roles in these pea aphid tissues.