A practical technique for electrophysiologically recording from lamellated antenna of scarab beetle

Host-plant volatiles play a key role in finding mate and suitable host plants of phytophagous scarab beetles. Hence it is immensely important to collect and identify these volatiles. The gas chromatography coupled with electroantennographic detection (GC-EAD) technique has been used as a rapid and convenient tool for the identification of physiologically active components from plants. Here, we describe a practical method for electrophysiologically recording from lamellated antenna of scarab beetles. This method enables direct electroantennogram (EAG) recordings from antennal club without damage to the antenna in a similar manner to the conventional cut-tip EAG recording technique for clavate antenna. The headspace volatiles from walnut (Juglans regia L.) trees were collected with a Poropak-Q trap at dusk and then analyzed with GC-EAD. Those volatile compounds that elicited electrophysiological responses on the antennae of a scarab beetle, Metabolus flavescens Brenske (Coleoptera: Scarabeidae: Melolonthinae) were determined by means of gas chromatography-mass spectrometry (GC-MS). The lamella directly connected to the recording electrode was held apart from the other two lamellae on the antenna with a minuten pin and a disposable syringe needle. In order to improve electrical contact, a surfactant, Tween® 80, was used to lower the surface tension of Beadle-Ephrussi Ringer solution. This study demonstrated that addition of 0.05% Tween® 80 to the Beadle-Ephrussi Ringer solution suppressed baseline noise and assured significantly greater EAG response in general. Due to its simplicity and efficiency, this method may also be useful for studying the electrophysiology of other insect species having club-like antennae.