Abstract:  As the largest group in the animal kingdom, insects have evolved complex sensory systems in response to various environmental stimuli, in which the chemosensation (olfaction and gustation) is the most important. The odorant receptors (ORs) and gustatory receptors (GRs) play a key role in olfaction and gustation, respectively. However, in recent years, it has been found that ionotropic receptors (IRs) are also involved in chemosensation as well as non-chemosensation such as sensation of temperature and humidity. The IR family is evolved from ionotropic glutamate receptors (iGluRs) which contain three typical transmembrane domains. Similar to ORs, each IR needs to be co-expressed with at least one of the four identified co-receptors (IR8a, IR25a, IR76b and IR93a) for its normal function. Two or more IRs can be co-expressed in a same olfactory neuron, and different IR combinations lead to their different response profiles in neurons. One insect species usually contains several to over one hundred IRs, with some IRs showing antennaespecific expression patterns, but most IRs remaining unknown in the function and the mechanism of action. In this article, the research advances in the structure and evolution of IRs, and the identification, expression and function of IR genes in insects were reviewed, hoping to provide some references for the further studies on the function and mechanisms of action of IRs, and the potential use of insect IRs as targets in pest control.

Key words:  Insect, chemosensation, ionotropic receptor, sensilla, olfaction, gustation