Diapause is frequently viewed as a developmental strategy unique to insects of the temperate zone. My primary objective in this review is to dispell this myth by presenting evidence for the widespread existence of diapause among tropical species. Although the environmental regulators are still poorly defined, I attempt to identify factors implicated in regulation and some of the special problems of diapause in the tropics. For purposes of this review I restrict my discussion to insects living within 200 of the equator, but clearly this is an arbitrary line. Winter in temperate zones presents a conspicuous obstacle, and a wealth of studies examine diapause as an adaptation to circumvent this inimical period. Reviews have focused on diapause physiology (72), endocrinology (19,31, 129), ecology (22, 24, 25, 115, 116), genetics (55), evolution (12, 33), thermoperiodism (6), clock mechanisms (5, 102), and cold tolerance (37, 101). Masaki's review on summer diapause (76) is especially relevant to this review because the warm summer of the temperate zone is much akin to the tropical environment. Although there are many definitions of diapause, I use the term to refer to an arrest in development that occurs at a specific stage. Egg, larval, pupal, and adult diapauses are all well documented, but for most species diapause can be expressed in only one stage of the life cycle. Diapause is programmed far in advance of the actual developmental arrest and thus differs from a simple quiescence that is an immediate response to adverse conditions. For some tropical species the information available is too sketchy to allow adequate