Document Type : Research Paper
Authors
1 Department of Landscape Engineering, College of Geography and Environmental Planning, University of Sistan and Baluchestan, Zahedan, Iran
2 Plant Protection Department, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran
Abstract
Keywords
Extended Abstract
Introduction
Diapause is a central seasonal life-history program in insects that allows populations to persist through predictable adverse periods such as winter cold, summer drought, or transient host scarcity. It is not a brief interruption, but an endogenous, genetically programmed alternative developmental and/or reproductive trajectory: it is initiated in advance of unfavorable seasons, maintained by coordinated neuroendocrine–endocrine control, and terminated so that development or reproduction can resume when conditions improve. The diapause phenotype often expresses a coherent “diapause syndrome,” including suppression of morphogenesis or gonadal maturation, reduced metabolic and respiratory demand, reallocation of resources toward storage and somatic maintenance, behavioral shifts and microhabitat selection, and enhanced tolerance to stressors such as cold, desiccation, and nutritional limitation. For herbivores and many agricultural pests, diapause therefore functions not only as a survival strategy but also as a seasonal timing mechanism that aligns key life-cycle transitions (adult emergence, oviposition, larval feeding) with narrow windows of host phenology and suitable microclimate. This timing role is especially consequential in univoltine species and taxa with obligatory diapause, where phenological mismatch can impose large fitness costs and shape outbreak dynamics.
This review synthesizes how environmental information is translated into diapause decisions and phase-specific physiology through neuroendocrine and endocrine signaling, and why mechanistic diapause biology is increasingly relevant to plant protection and integrated pest management (IPM) under climate-driven variability in thermal and moisture regimes. We integrate three complementary layers: (i) operational definitions and diagnostics that reduce misclassification; (ii) a process-based view of diapause organized into ecophysiological phases; and (iii) implications for phenology forecasting, monitoring design, and intervention timing.
A prerequisite for mechanistic inference and reliable forecasting is distinguishing diapause from other forms of dormancy, particularly quiescence. Dormancy broadly denotes reversible reductions in activity or development. Diapause is initiated within a species- and stage-specific sensitive window (decision point) in response to seasonal “token cues”—most commonly photoperiod and temperature—and it can persist even if short-term conditions temporarily improve. In contrast, quiescence is typically a short-term, exogenous arrest that tracks immediate environmental constraints and resolves rapidly once constraints are removed. Conflating these states is not merely semantic: it can bias experimental interpretation of endocrine regulation and introduce systematic error into field predictions of emergence and vulnerability windows. A recurrent pitfall is post-diapause quiescence, in which internal diapause constraints have been lifted but unfavorable external conditions still prevent renewed activity. Robust diagnosis should therefore rely on convergent evidence—developmental or reproductive status, standardized reversibility assays, metabolic or respiratory proxies, and endocrine/molecular indicators where available—rather than immobility alone.
To move beyond binary thinking, we frame diapause as a dynamic trajectory organized into ecophysiological phases: induction, preparation, initiation, maintenance, termination, and often post-diapause quiescence. This phase structure explains why externally similar individuals can occupy distinct internal states, why termination does not necessarily imply immediate emergence, and why rates of “diapause development” can differ among environments and seasons. Importantly for applied entomology, susceptibility to control measures and the reliability of phenology models can vary across phases, making phase awareness essential for translating biology into decision support.
We then review the environmental inputs that shape diapause decisions and their translation into endocrine outputs. Photoperiod—often encoded as night length—serves as a reliable seasonal calendar cue in many temperate insects. Temperature acts both as a modifier of photoperiodic sensitivity and thresholds and as a direct regulator of rate processes, including diapause development and termination kinetics. In some systems, thermoperiod–photoperiod interactions and the timing of thermal inputs within the light–dark cycle are decisive. Nutritional cues and host quality can shift diapause thresholds, particularly in herbivores experiencing seasonal changes in plant chemistry and in host–parasitoid networks where host condition covaries with season. Moisture and humidity are less universal than photoperiod but can be critical in taxa adapted to dry seasons or in species with drought-resistant diapausing eggs, where survival and hatching integrate combined temperature–humidity histories.
Mechanistically, environmental information is integrated by neuroendocrine circuits that interact with circadian and/or photoperiodic timing systems and are executed via endocrine axes. Across diverse insects, diapause is commonly associated with modulation of juvenile hormone and ecdysteroid signaling, reconfiguration of insulin/insulin-like signaling and FOXO activity, and coupling to nutrient-sensing pathways such as TOR and AMPK. Together, these networks implement the core diapause logic: suppressing growth, metamorphosis, or reproductive maturation; lowering metabolic demand; reallocating resources toward storage and maintenance; and elevating cellular and organismal stress resistance.
From a plant-protection perspective, diapause is often the hidden driver behind failures of calendar-based control. Many major pests overwinter or oversummer in stages that are difficult to target (e.g., soil-dwelling larvae, diapausing pupae, sheltered adults) and synchronize emergence so that susceptible stages occur in brief windows. Degree-day models remain essential, but they can be unreliable unless diapause processes are represented explicitly. Diapause-informed phenology models that incorporate induction thresholds, temperature-dependent diapause development, and termination kinetics can improve forecasts of spring timing, voltinism, and pest–host synchrony under variable winters and increasing thermal fluctuations. Predictive performance can be strengthened further by integrating mechanistic models with field monitoring (e.g., trap time series) using cumulative-emergence approaches that translate weather histories into actionable estimates of stage occurrence and population pressure.
In summary, diapause sits at the intersection of seasonal insect biology and IPM decision support. It determines when pest populations reappear, how tightly risk windows are compressed, and how sensitive population timing is to climate-driven shifts in temperature regimes and host phenology. By unifying cue ecology, neuroendocrine–endocrine control, and phase-based diapause development, this review provides a practical framework for accurate diagnosis, improved forecasting, and more targeted interventions in agricultural and forest systems.
All authors contributed equally to the conceptualization of the article and writing of the original and subsequent drafts.
No new data were generated or analyzed in this study. All information is available in the cited literature.
We acknowledge the financial support (No. 99017766) for this project from the Iran National Science Foundation (INSF).
Ethical consideration
The study was conducted on plant-pathogen fungus and beneficial entophy-
tic bacteria that are abundant in the environment and do not require ethical approva
Not applicable. This study is a narrative review and did not involve experiments on humans or vertebrate animals.
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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