A storage protein gene, CsSP2, was cloned and sequenced from the rice stem borer, Chilo suppressalis. Analysis of the cDNA sequence revealed an open reading frame of 2,118 bp in length which encodes an arylphorin-like protein with a calculated molecular weight of 83.7 kDa. The expression level of CsSP2 was higher in non-diapausing larvae than in diapausing larvae at 20 degrees C. When diapausing larvae were acclimatized in a stepwise fashion from 20 degrees C to 5 degrees C, CsSP2 expression was up-regulated five days after acclimation at 15 degrees C. The level was maintained for 10 days after acclimation at 5 degrees C and down-regulated thereafter. Some up-regulation in CsSP2 expression was detected in the post-diapause state. In non-diapausing larvae, CsSP2 expression was down-regulated in the course of cold acclimation. Protein products of CsSP2 might have an important role as an amino acid reservoir or a cellular defense mechanism during diapause.