Injection is a technique widely employed to manipulate functional processes in honey bees. Injections have been performed at different stages of the honey bee life cycle, from early embryos to adults (Lozano et al., 2001; Aase et al., 2005; Kucharski et al., 2008). In adult honey bees, the injection of receptor antagonists into the brain or antennal lobes provided insights into pathways involved in memory formation and retrieval (Lozano et al., 2001; Farooqui et al., 2003; Wright et al., 2010). Gene expression can be manipulated by injecting double stranded RNA (Schlüns and Crozier, 2007; see also Section VI – RNA interference). Injections of pathogens (Wilson and Rothenbuhler, 1968) and insecticides (Bendahou et al., 1999), as well as injection of labelled markers to trace substance distributions (Crailsheim, 1992) are further applications.
Irrespective of the substance being injected, rupturing the cuticle with the needle is invasive and causes an immune response in honey bees, including increased expression of the immune response gene Defensin2 and antimicrobial peptide production (Richard et al., 2008; Laughton et al., 2011). In addition, researchers should be aware that handling during injection induces a stress response and the tissue damage further poses a risk of secondary infection (Kucharski and Maleszka, 2003). The stress and immune response may even result in death of injected individuals. In adult A. mellifera, a 20% mortality rate was observed within 48 h of injection with control buffers (Picard-Nizou et al., 1997). Most studies do not report survival rates following injection, but immune responses and mortality risks should be considered when choosing to inject substances.