Insect olfaction

Insect olfaction refers to the function of chemical receptors that enable insects to detect and identify volatile compounds for foraging, predator avoidance, finding mating partners (via pheromones) and locating oviposition habitats. Thus, it is the most important sensation for insects. Most important insect behaviors must be timed perfectly which is dependent on what they smell and when they smell it. For example olfaction is essential for hunting in many species of wasps, including Polybia sericea.

The two organs insects primarily use for detecting odors are the antennae and specialized mouth parts called the maxillary palps. Inside of these olfactory organs there are neurons called olfactory receptor neurons which, as the name implies, house receptors for scent molecules in their cell membrane.The majority of olfactory receptor neurons typically reside in the antenna. These neurons can be very abundant, for example Drosophila flies have 2,600 olfactory sensory neurons.

Insects are capable of smelling and differentiating between thousands of volatile compounds both sensitively and selectively. Sensitively is how attune the insect is to very small amounts of an odorant or small changes in the concentration of an odorant. Selectivity refers to the insects ability to tell one odorant apart from another. These compounds are commonly broken into three classes short chain carboxylic acids, aldehydes and low molecular weight nitrogenous compounds.

Insects have been used as a model system to study mammal and especially human olfaction. Yet, unlike vertebrates who use G protein coupled receptors (GPCRs) insects ORs (olfactory receptors), GRs (gustatory receptors) and IRs (ionotropic receptors) are all heteromeric ligand-gated ion channels. Much like in vertebrates, axons from the sensory neurons converge into glomeruli. But they differ in where the glomeruli are housed. In mammals they are located in the olfactory bulbs but are in the antennal lobe of insects.

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