10.1. Introduction

RNA interference (RNAi) is a cellular mechanism leading to a knock-down of gene expression mediated by target specific double-stranded RNA (dsRNA) molecules (Fire et al., 1998).  Understanding the mechanism of mRNA destruction by these dsRNA molecules dramatically increased the possibilities of functional genomics studies during the last decade especially in organisms where the recovery of mutants is not feasible. Thus RNAi has become a dominant reverse genetic method for the study of gene functions and furthermore, plays an increasing role in therapeutics and in pest control (Maori et al., 2009; Liu et al., 2010; Hunter et al., 2010).

Up to now a dozen studies report on the successful usage of RNAi in honey bees. But the application methods and also the choice of RNAi effective molecules are very diverse. Several studies report on the application of dsRNA to eggs and larvae whether by injection (Aronstein and Salivar, 2005; Beye et al., 2002; Maleszka et al., 2007) or ingestion (Aronstein et al., 2006; Patel et al., 2007; Kucharski et al., 2008; Nunes and Simoes, 2009; Liu et al., 2010). Others report on a successful manipulation of adult bees (Amdam et al., 2003; Farooqui et al., 2004; Seehuus et al., 2006; Schlüns and Crozier, 2007; Maori et al. 2009; Paldi et al., 2010; Mustard et al., 2010; Jarosch and Moritz, 2011; Jarosch et al., 2011).

This section aims at a collection of RNAi protocols successfully applied in honey bees beforehand. The well-established protocols for producing dsRNA as well as siRNA (short interfering RNAs, the products of dsRNA once the enzyme Dicer and its partners have processed them) molecules are presented. Moreover, the two application methods feeding and injection are presented and compared to each other.  In conclusion, we summarize five important factors that may decrease the effectiveness of target gene expression knock-down.