3.1. Introduction

Honey bees produce airborne volatile organic compounds which serve as indicators of the ‘status’ of the colony. As such, the collection, analyses, bioactivity of identified honey bee odours is vital to understanding how social cohesion is maintained, regulated and influenced by various biotic factors such as foreign intruders (Torto et al., 2005, 2007a, 2007b) and pathogens (Swanson et al., 2009). Odours associated with honey bees have been used to improve colony vigour and to manage certain pest such as the small hive beetle Aethina tumida, (Teal et al., 2006; Arbogast et al., 2007; Torto et al., 2007b).

A specialized method that provides information on honey bee detection and sensitivity to specific compounds is coupled Gas Chromatography-ElectroAntennographic Detection (GC-EAD) (Schneider, 1957; Baker et al., 1985; Torto et al., 2007a; Swanson et al. 2009). This coupled system uses an insect antenna in tandem with a flame ionization detector (FID) to link the electrical activity stemming from neurons signalling receptor binding of chemicals to individual peaks.  GC-EAD is an excellent analytical tool but works best for chemicals detected by many receptors thereby producing a strong electrical stimulation from the antenna. In this hybrid method, volatiles emerging from a GC column are split between a conventional GC detector (chemical sensor) and an antenna mounted between two electrodes (biological sensor). The interpretation of detected compounds requires an understanding of insect physiology, since antennal stimulation to chemicals represents activity which may indicate attraction or repellence. Some chemicals may be detected by a single receptor, transmitted by a single neuron and then amplified in the brain while others may stimulate several receptors and their associated receptor neurones. Honey bee chemosensory organs can be much more sensitive to bioactive compounds than analytical detectors, sometimes leading to strong electrophysiological responses to correspondingly weak chemically (FID) detected components. Although the honey bee antenna is most commonly used, other body parts having chemosensory activity can be used as biosensors. Antennae and body parts with weak electrophysiological activity can have their activity amplified by mounting multiple parallel sensory organs in tandem across a single electrode.

This section focuses on methods to collect honey bee odours outside of the colony environment (ex-situ volatile collection) and to carry out electrophysiological recordings using antenna or other chemosensory body parts of the honey bee.