Chemosensory proteins are a class of small (10-15 kDa), soluble proteins characterised for the first time by Angeli et al. (1999) as secreted into the sensillar lymph of insect chemosensory sensilla

Sensilla

A sensillum is an insect sensory organ protruding from the cuticle, or sometime lying within or beneath it. Sensilla are divided in chemical, mechanical , thermal and visual....

. Some members of CSPs were already discovered in Drosophila

Drosophila

Drosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" or more appropriately pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit...

, and other insects, although not clear link with olfactory or gustatory function was assigned.
In the last years CSPs were found in insect contact and olfactory sensilla, but other members showed peculiar functions.