RNA interference (RNAi) is a powerful method to inhibit gene expression in a sequence specific manner. Here, we described the development of RNAi by micro-injection of double-stranded RNA ( dsRNA) in the pea aphid Acyrthosiphon pisum. Injection of dsRNA into whole aphid body induced the silencing of two marker genes with different expression patterns: the ubiquitously expressed Ap-crt genes encoding a calreticulin and the gut specific Ap-cath-L gene encoding a cathepsin-L. Time-course analysis of the silencing showed similar temporal patterns for both genes: inhibition started at 1 day after injection, reached its maximum at 5 days and stopped at 7 days. A comparable 40% decrease of gene expression was observed for Ap-crt and Ap-cath-L. The pea aphid is the first Hemipteran insect for which genome sequence will be available soon. The gene knockdown technique developed in this study will be an essential post-genomic tool for further investigations in aphidology.