Anatomy and Functioning of the Insect Chemosensory System

Abstract

Semiochemicals play a major role in insect ecology, as evidenced by the broad distribution of chemosensory structures on the insect body. Substantial progress has been made in the field of insect olfaction and taste in recent years. Soluble carrier proteins, receptors, neurons and circuits have been described in considerable detail, and the mechanisms by which they bind, detect, encode and process chemosensory stimuli are being unravelled. At the periphery, chemosensory neurons situated in dedicated sensilla detect and encode the properties of chemical signals thanks to receptor proteins. Insects have evolved large repertoires of such receptors that are genetically and structurally unrelated to their vertebrate counterparts. They are classified into three major families: odorant receptors (for olfaction), gustatory receptors (for taste), and ionotropic receptors (for both). In fact, all are ionotropic (i.e. functioning both as receptors and ion channels), which enhances the speed of odour detection. The encoded signal is transmitted to brain structures where it is processed and translated into a given behaviour. These behaviours exhibit some plasticity according to age, feeding state, circadian rhythm, mating status, etc. The underlying neural and endocrine mechanisms of this plasticity concern both peripheral detection and central nervous integration.