Controversial aspects of diapause development

Abstract

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 com munity, 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 proc esses), 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 acti vation 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 ade quately wide and less affected by a priori assumptions. Stimulation by temperature increase or improvement in food or other condi tions 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.

Effects of Temperature and Photoperiod on the Termination of Larval Diapause in Lucilia sericata (Diptera: Calliphoridae)

“…However, the requirement of low temperature for the completion of diapause development has been overgeneralized (Hodek and Hodková, 1988). In many species, diapause terminates spontaneously under the conditions above a lower thermal threshold (Tauber et al , 1986;Danks, 1987;Hodek and Hodková, 1988;Hodek, 2002). In L. sericata also, larval diapause terminated spontaneously when kept continuously under the diapause-inducing condition of 20 ° C and LD 12:12, although pupariation was not synchronized.…”

“…Diapause in many temperate insects can be terminated by photoperiod and high temperature as well as low temperature (Tauber et al , 1986;Danks, 1987;Hodek and Hodková, 1988;Hodek, 2002). In Lucilia , Ring (1968) has surmised that photoperiod is unlikely to play an important role in the termination of diapause, with no evidence supporting this assumption.…”

Pattern of Pink Bollworm Diapaused Larval Exit from the Last Season Cotton Bolls and Their Biological Parameters

“…As evidenced by characteristic temporal patterns of gas exchange, nutrient metabolism, stress resistance, and gene expression, diapause is a dynamic process. Besides that, environmental and hormonal regulators of diapause have been reasonably well defined (Denlinger, 2002;Hodek, 2002). Diapausing insects pass through a graded series of physiologically distinct developmental stages including induction, preparation, initiation, maintenance, termination, and sometimes post-diapause quiescence (Kostal, 2006).…”

Interspecific Variation in Size, Diapause Intensity, and Moisture Responses of First-InstarSpeyeria(Lepidoptera: Nymphalidae) Larvae

“…One species (S. nokomis) has a diapause more similar to "quiescence" (Tauber et al 1986, Danks 1987. In most species, normal diapause termination appears to require an interval of exposure to low temperatures (Mattoon et al 1971, Hodek 2002, James 2008. In this study, species with stronger diapause, and possibly longer low-temperature termination requirements, suffered higher mortality under "forced" diapause termination conditions.…”