3.3.1. Setup

Electrophysiological studies require expensive specialized equipment including software, which can be purchased from commercially available sources. A basic electrophysiological setup consists of four elements (Syntech, 2004).

  • A biological sensor which is usually an antenna or any other chemosensory organ mounted across a pair of electrodes.
  • Amplifier and signal processing electronics specially built to minimize noise and to control the baseline signal.
  • Signal display and recording system which makes use of computer software for display, record and analysis of signals.
  • Stimulus application system which ensures a continuous or discontinuous release of test stimuli over the antenna while its electrical activity is being measured.

Equipment similar to that described by Torto et al. (2005) can be used to measure bee antennal responses to various chemicals. A stimulus source consisting of an inert metallic delivery tube (Fig. 5a) with a hole at is basal end originating from the side of a gas chromatograph serves as the channel via which volatile stimuli are applied over the mounted antenna on a micro-manipulator or gel probe (Syntech, 2004). The micro-manipulator has two terminals; an indifferent and a 10x amplification recording terminal. Both terminals containing silver wires (0.1 mm in diameter) are sheathed with capillary tubes tapered at one end by drawing them out as heated tubes in pipette pullers, filled with insect saline solution such as Ephrussi solution (consisting of an aqueous mixture of Na, K, Mg, Ca and Cl) (Christensen, 2004), thereby converting them into conducting electrodes (Christensen, 2004). The manipulator base is connected to an earth cable to minimize internal electrical interference while its recording electrode is connected to an AC/DC-EAG amplifier. Signals from the recording electrodes are amplified and digitized by data acquisition electronics. This electronic equipment acquires signals from the amplifier and transforms them into digital wave-like signal depicting antennal responses as peaks recorded in millivolts (mV). Signal visualisation, recording and analysis is carried out using a specific software (e.g. GC-EAD, Syntech) installed on a personal computer (PC). All the EAD equipment except for the gas chromatograph, data acquisition electronics and PC are enclosed within a Faraday’s cage to reduce external electrical interference. For more details of the setup, see the system’s manual (e.g. Syntech, 2004).

Fig. 5a. (a) The stimulus delivery line for the column effluent, (b) humidified air supply used to flush column effluent in the background (blurred), (c) Saline-filled glass electrodes (d) a mounted bee antenna showing both head and antenna (e) mounted electrode holders.