The method, protocol describes a technique of how to prepare double-stranded RNA (dsRNA) for RNA interference in Drosophila by synthesis of individual RNA strands from linearized plasmid templates, followed by annealing of the strands.  DsRNA molecules with a length of 500-800 bp seem to be most active.  The dsRNA can be made from cDNA or genomic DNA templates, as long as most of the dsRNA corresponds to presumptive exon sequence.

Protocol: Synthesis of dsRNA for RNAi in Drosophila: Plasmid Template Method Protocol