Neurobiology of Pheromonal Signal Processing in Insects

Abstract

The basic mechanisms by which an insect detects an odorous signal has intrigued investigators since Fabre (1879) reported the attraction of male moths to females. Modern progress in the elucidation of these mechanisms has closely followed advances in electrophysiological, morphological, biochemical, and molecular biological techniques. At theperipheral leveldevelopment of electrophysiological techniques allowed for recording of odor-stimulated responses from whole antennae (Schneider and Hecker 1956; Schneider 1957) and from single sensilla either by using sharpened tungsten electrodes (Boeckh 1962) or by clipping tips of individual sensilla and recording electrical responses with electrolyte-filled glass capillaries (Kaissling 1974). Concurrent morphological studies allowed investigators to correlate whole antennal odor responses with the presence or absence of sensillar types and also to correlate the number of action potential types recorded with the number of neurons within a given sensillum (Boeckh et al. 1965). In male moths, trichoid sensilla were shown to have individual receptor neurons specialized for detection of a female-produced sex attractant pheromone component (Boeckh et al. 1965) or interspecific inhibitor (Grant et al. 1988). The ability of pheromone receptor neurons to respond to pulsed stimuli correlated with the ability of the insect to detect and respond to the temporal and spatial nature of filamentous odor plumes (Kaissling 1986b; Rumbo and Kaissling 1989; Borroni and O’Connell 1992) as revealed from the study of charged ions in nature (Murlis 1986; Murlis et al. 1992).