In contrast to the exceptional diversity of semiochemical-regulated behavior in the insects, chemical communication in the Acari is restricted to a few limited roles. These include clustering, mate-finding processes, host- and food-finding processes, and dispersal. No evidence of pheromones regulating oviposition, necrophoric behavior, recognition of hive mates, or many other processes found in numerous insect groups has been reported in the Acari. Perhaps the most noteworthy feature of acarine pheromones or allomones is the use of the same or similar molecules by many species. Metastriate ixodids use volatile phenols to regulate courtship behavior and, in at least one species, feeding site selection and attachment as well. Argasid ticks use a water- or saline-soluble assembly pheromone, which appears to represent a single type of compound, if not the identical compound in all cases. Acarid mites use terpenoids as alarm pheromones and allomones, while certain phytoseiid and tetranychnid mites use terpene alcohols as arrestant sex pheromones. Another notable feature of acarine pheromones is the use of multicomponent signals to regulate different events in the behavioral process. Thus, two separate sex pheromones are necessary to successfully complete courtship in certain Dermacentor ticks, while three pheromones appear necessary to complete feeding-site selection, attachment, and clasping in certain Amblyomma species. In other cases, a combination of chemical and physiological signals is used to regulate courtship. Although the same or similar compounds may be used for chemical communication, no universal model describes the behavior of all species in an acarine family or order. Species-specific differences in perception of pheromone concentration, molecular composition, aphrodisiacs, and other selective signals facilitate species isolation, even though the initial steps in the behavior are similar in all species. This combination of unity and diversity allows economy in the biosynthesis of semiochemicals without compromising species integrity. In the brief period following the pioneering discoveries of pheromones in ticks (8) and mites (16, 17), evidence of a variety of acarine semiochemicals has been obtained, several pheromones and allomones have been identified, a sex pheromone gland has been described, and considerable effort has been directed to understanding the regulation of pheromone activity. Nevertheless, our knowledge of communication in this large and exceptionally diverse group is meager.(ABSTRACT TRUNCATED AT 400 WORDS)