Recent GS-MS and GC-EAD studies of pheromone production and perception in caddis-flies and lower moths have shown that these insects use rather limited selection of volatiles as attractants. Most of these attracting volatiles are alcohols and ketones, although the diversity of chemicals produced by sternal glands of the 5th abdominal segment is much wider, especially in the lower Trichoptera. Sternal pheromone glands produce only short-chain polymers in all Amphiesmenoptera. These glands are part of the ground-plan for the related orders, Trichoptera and Lepidoptera, occurring in both sexes and producing similar but not identical set of components in males and females. The presence of pheromone volatiles is shown to be restricted to gland segments (fig. 1), although some other short-chain polymers do occur in female head of Molanna angustata (Molannidae). The compositions of pheromone blends in lower Trichoptera (Glossosomatidae, Rhyacophilidae, Philopotamidae) are multi-component and resembling the plant volatiles. A proposed hypothesis on the origin of the pheromone communication postulates the basic resemblance of early pheromones and plant volatiles in variety and chemical composition. These pheromones were perceptible by non-specialized receptors of the Amphiesmenopteran ancestor and served as guides for insect aggregation on plants as well as on water body shores, marking the places suitable for wide variety of species. The primary aggregation function of pheromones has been changed in more advanced communication systems to the species-specific signaling with sex-related asymmetry of signals, although the aggregation significance persisted in some species. The pheromone communication disappears in some most advanced lineages (e. g., Leptoceridae) with parallel reduction of glands, secretion, and antennal receptors. Changes in pheromone composition do not show gradual divergent evolution in related species; instead, the saltation transformations of pheromone blends with persistence of major components in remote families seem to be the typical case.