4. 1. Introduction
Biogenic amines have a variety of roles in the lives of insects, acting as neurohormones, neuromodulators, and neurotransmitters that can influence both behaviour and physiology (reviewed in Blenau et al., 2001; Scheiner et al., 2006). Four biogenic amines, dopamine (DA), octopamine (OA), serotonin (5-hydroxytryptamine, or 5-HT), and tyramine (TA), have been identified as being significantly associated honey bee behaviour and may be responsible for orchestrating the complex division of labour within their colonies (Fuchs et al., 1989; Brandes et al., 1990; Harris and Woodring, 1992, 1995; Taylor et al., 1992; Bozic and Woodring, 1998; Wagener-Hulme et al., 1999; Scheiner et al., 2002, 2006; Schulz et al., 2002; Barron and Robinson, 2005; Fussnecker et al., 2006; Agarwal et al., 2011). Several approaches have been used to measure amine concentration in insect central nervous system tissues (histofluorimetry, immunohistochemistry, radioenzymatics, gas chromatography-mass spectroscopy), but one that has been used most frequently in honey bees is high performance liquid chromatography coupled to electrochemical detection (HPLC-ECD). This approach utilizes a carrier solution, referred to as the mobile phase, to bring the sample across a filter column and then to the detector. HPLC-ECD analysis can be very sensitive and provide robust and repeatable results. The primary issue with this approach is that HPLC systems can be difficult to maintain over time, necessitating the processing of samples in small batches and running calibrating standards frequently.
An important caution with any approach used to quantify biogenic amines is that their levels can change rapidly in bees subjected to any of a variety of environmental perturbations (Harris and Woodring, 1992; Harris et al., 1996; Chen et al., 2008). For that reason the handling time when collecting samples should be as short as possible, and then technique used should be very uniform. In addition, these amines are highly sensitive to light and heat, therefore every precaution should be made to keep samples cold and covered prior to analysis.