Diapause is defined as a state of developmental arrest in which the arrest is established by a physiological mechanism rather than by simultaneously unfavorable environmental conditions (Beck, 1962). To guarantee the continuity of life it is necessary that single cells and entire organisms can survive in ideal environments, but also in conditions of scarcity. When conditions are not suitable for procreation, many cells have the ability to enter a non-dividing state, while maintaining the ability to re-enter the proliferative cell cycle. Diapause is a state of dormancy in which a reversible arrest of the cell cycle occurs, capable of protecting against numerous environmental adversities. Diapause has been recorded in insect species ranging from the European corn borer, as discussed by Staley D. Beck (1962), to the monarch butterfly (Herman 1981). Although diapause is not directly maintained by environmental factors, diapause is induced and sometimes terminated as a response to environmental stimuli. The most common environmental stimulants are temperature (Cherill & Begon, 1989) and day length (Beck, 1962). These organisms enter diapause due to the many advantages it offers to the insect's existence, including waiting for the perfect time to reproduce or avoiding predators (Herman, 1981). From an evolutionary perspective, the ability to engage in diapause is crucial to an insect's ability to adapt and survive in its environment. Evidence of diapause has been collected from a variety of insect species in which diapause is induced by environmental stimuli and consequently individuals benefit in multiple ways. As a result of the benefits of diapause, many insect species have evolved the ability to undergo a state of dormancy. There... in the middle of the paper... many results were tested and obtained. One of the conclusions reached is that photophase:scotophase ratios have a great influence on the relationship between photoperiods and dormancy. Diapause with 24-h photoperiods approached a maximum when the photophase:scotophase ratio was approximately 1:1, and approached a minimum at ratios of 1:2 or 2:1. Diapause in photoperiods showing different photophase:scotophase ratios is shown in Table I (fig. 1). This experiment required the use of constant temperature BOD incubators that had been modified to include a thermistor temperature control system to maintain constant temperature regardless of the duration of the photophases. Day length has a strong correlation with temperature in nature, so it was critical that both of these variables were controlled for in Beck's study.