Amylase activity in honey bee hypopharyngeal glands reduced by RNA interference

Double-stranded RNA (dsRNA) has been found to interfere with gene expression in various species, a phenomenon known as RNA interference (RNAi). We show here that RNAi is effective in reducing gene expression in the adult honey bee (Apis mellifera). A 1175 bp fragment of the hypopharyngeal amylase gene from the honey bee was cloned into a modified pGEM-5Zf(+) vector. The gene fragment was inserted between two opposing T7 promotors, thus enabling expression of dsRNA specific for the amylase gene when the plasmid was grown in an Escherichia coli strain expressing T7 RNA polymerase. This dsRNA was introduced into the haemolymph of forager honey bees by intra-abdominal injection and the effects on amylase activity in the hypopharyngeal glands of those bees examined. Compared to controls, injection of amylase gene dsRNA produced a significant decrease in amylase activity of 27.5% 3 days post-injection (P = 0.001). An experiment using radiolabelling to follow the fate of the dsRNA, revealed that most of the radioactive RNA was lost from the haemolymph within 24 h, probably sequestered into cells. In this experiment, bees injected with amylase gene dsRNA showed a reduction of 80% of amylase activity 24 h post-injection (P = 0.001). This indicates that the maximum effect of the amylase gene dsRNA in bees is probably greater than demonstrated in our initial experiment, and that the effect is short-lived. Here we demonstrate that RNAi is effective in reducing gene expression in Hymenoptera in distant organs following intra-abdominal injection of adult bees.