Measuring Pheromone Dispersion in the Field with the Single Sensillum Recording Technique

Abstract

Pheromones are active at extremely low concentrations. Under natural conditions, airborne pheromones are embedded in a background of many other volatiles. Direct measurement of pheromone components in the field is not possible with currently available physicochemical detection techniques, because of the limited sensitivity and the lack of specificity of these techniques. However, sensitive and selective pheromone receptors are present on the antennae of many insect species. With the help of electrophysiological recording techniques, these receptors can be used as biological detectors. Two of these techniques are well established: electroantennography (EAG) and single sensillum recording (SSR). Because of the rather complex instrumentation, both methods were employed exclusively until recently in laboratory settings. The EAG technique was first used in the field by Baker and Haynes (1989) in a stationary setup, in which the antennal preparation was freely exposed to the air. In 1990 Koch described a transportable EAG apparatus, in which the antenna was conditioned by a continuous filtered airflow interrupted by exposures to the surrounding air and reference sources. This device was used to measure relative pheromone concentrations (Milli and de Kramer 1989; Karg et al. 1990; Sauer et al. 1990; Sauer 1991; Milli and Dickler 1992; Sauer et al. 1992) under various field conditions (Bengtsson et al. 1994; Karg et al. 1994) and in wind tunnels (Färbert et al. this volume). The method used by Baker and Haynes (1989) allows registration of fast fluctuations (<1 sec) of pheromone concentrations, but the antenna is not shielded from air turbulence and nonpheromone volatiles. In the device designed by Koch (1990) the airflow over the preparation is kept constant and the effect of nonpheromone volatiles is canceled by a special measuring protocol and the use of reference sources. As a consequence of this method, the device produces data about pheromone concentrations and concentration gradients in space, but fast fluctuations in concentrations cannot be recorded.