The insect olfactory system shares many features with the vertebrate system and has been studied as an excellent model for olfactory information processing. Olfactory receptors have been identified molecularly and functionally and olfactory glomeruli have been revealed as functional units of the first order olfactory center. These findings have led to the understanding of so called “labeled line” processing and “combinatorial coding” as basic functions for olfactory processing. Recently, progress in research using Drosophila melanogaster has revealed detailed functions and circuit organizations for olfactory processing, especially with the understanding of the circuit structure of higher brain centers, changing our view of the olfactory processing. Recent findings have revealed the complete circuits of sex pheromone processing, innate odor valence representation, labeled line processing for ecologically relevant odors, dopamine modulation at the mushroom body output compartments and the comprehensive identification of lateral horn neurons. Here we review pheromone and general odor processing from the antennal lobe through higher brain centers such as the mushroom body and lateral horn to the behavioral output, with special reference to recent progress on the research in moths and fruit flies.

Euryhaline fishes living in brackish water have physiological mechanisms of osmoregulation and select environmental water with suitable salinity. Compared with the physiological mechanisms, there is limited information for behavioral acclimation for the salinity selection. One major reason why is that it is technically difficult to measure salinity experienced by fish. In this paper, we present the methods to measure salinity on free-ranging fish using with two conductivity loggers (geolocator and ORI400-DTC). The geolocator can discriminate whether a tagged fish migrated to freshwater region because it is energized only in salt water. ORI400-DTC can accurately record conductivity in addition to water depth and temperature at one second intervals. One of the loggers was attached to a black seabream (Acanthopagrus schlegelii), one of major euryhaline fishes in coasts of Japan. The result of geolocator showed that the fish did not migrate to freshwater region for the entire recording of 4-day period. The result of ORI 400-DTC showed that the fish spent 48% of time for 3-day recording period in hypotonic water lower than the body fluid. In addition, the data suggested that the thermocline and halocline formed at near a depth of 1 m may affect the migrate behavior of the black seabream. We believe that application of ORI400-DTC is effective to understand behavioral acclimation of various euryhaline fishes migrating to brackish water. It is also expected that the geolocator can be applied to investigate migratory behavior of diadromous fishes entering freshwater regions.