Abstract
Although some parts of diapause development have been clarified up by endocrinologists, knowledge of the underlying processes remains insufficient. The survey of ecophysiological aspects of diapause development has thus to be limited to inputs and outputs from the blackbox. The terms diapause development, diapause intensity, post-diapause quiescence, horotelic processes of diapause, and tachytelic processes of diapause (reactivation) are defined. Andrewartha's term diapause development has been accepted because it shows diapause as a dynamic event.In about the last 20 years, some views on diapause development have been updated, while others have fossilised. The assumption that chilling is a general prerequisite for completion of diapause development in all insects still survives in part of the scientific community, in spite of much contradictory evidence and often due to inadequate interpretation of experiments (examples given in figures and tables). On the contrary, it has been generally recognised that in temperate climates overwintering diapause is usually already completed in early/mid winter and the dormancy is then temperature quiescence. The conception of multiple pathways of diapause completion postulates that diapause can be completed either by the normal (slow) progress of diapause development (horotelic processes), or by a faster activation (tachytelic processes). There are important differences between the mechanisms regulating activation and the horotelic processes. Thus, e.g., the photoperiodic response is lost during horotelic completion, while after photoperiodic activation it persists. In addition to photoperiodic activation other kinds of activation are being studied, particularly activation by high temperature.Some conclusions can be made from modern studies on diapause development. In every individual, several (at least two) possible pathways exist that are evidently interlinked and mutually complementary. Thus the time of diapause passed at any condition has to be considered, as well as the exposure to very low temperatures. In temperature studies the experimental range ought to be adequately wide and less affected by a priori assumptions. Stimulation by temperature increase or improvement in food or other conditions has to be considered.The success of diapause completion should be measured by at least four parameters: (1) incidence (%) of developmental steps; (2) duration of delay; (3) synchronization; (4) vigour of post-diapause insects (shown by long-term survival or fecundity). The last two parameters have usually been neglected.
Highlights
Instead of repeating the information already pub lished in a short history of ecophysiological diapause studies (Hodek, 1999), the focus here will be on several problematic aspects of diapause development
While Pyrrhocoris apterus adults remain sensitive to photoperiod and dis continue egg laying at short days early after the photope riodic activation (Fig. 3A), the horotelic completion of diapause results in a loss of photoperiodic response, i.e. egg laying is maintained at short days (Fig. 3B) (Hodkova & Hodek, 1989)
For the adult winter diapause of spring breeders most authors have accepted that diapause is completed in the field after 4 to 5 months after induction, and changes into quiescence, during which morphogenesis is hindered just by low ambient temperatures (Table 1). According to this generally accepted view, and in contrast to laboratory experiments on photoperiodic activation of winter diapause, and in contrast to estivation diapause, there is usually no cue or stimulus terminating diapause, the course of diapause development may be modified by some factors, such as temperature more or less close to the optimum for horotelic processes
Summary
While Pyrrhocoris apterus adults remain sensitive to photoperiod and dis continue egg laying at short days early after the photope riodic activation (Fig. 3A), the horotelic completion of diapause results in a loss of photoperiodic response, i.e. egg laying is maintained at short days (Fig. 3B) (Hodkova & Hodek, 1989). They concluded that (1) the eggs require high tempera tures for a rapid termination of “the late stage” of dia pause; and (2) low temperatures are not a requisite for the completion of diapause, they are favourable for “the early stage” of diapause.
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