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Diapause

An insect entering diapause is not responding to winter. It is predicting it, from daylength, sometimes a generation before the winter arrives.

Diapause is a dormancy committed to in advance. It is triggered by daylength — a cue that carries no hardship of its own — often weeks before conditions worsen and sometimes a generation ahead, and an insect in diapause moved somewhere warm and well-fed simply stays in diapause.

Everything else on these pages is a response. Diapause is a prediction, and that single difference reorganises how it works. The insect is not waiting for the cold to arrive; it is reading daylength in late summer, while conditions are still excellent, and using it to forecast a winter it has never experienced. Daylength is the right cue for this precisely because it is uninformative about the present — it is the same every year, unaffected by a warm autumn or a mild week, and therefore reliable in a way that temperature is not. The commitment is deep. An insect that has entered diapause and is then given warmth, food and long days does not resume development; it stays put until an internal programme completes, which in many species requires a long period of chilling first. This is genuinely counter-intuitive and it has practical consequences: it is why you cannot force many insects out of diapause by simply bringing them indoors, and why cold storage is part of how diapause is broken in the laboratory. It also explains a long-running confusion in the literature, where different papers reported apparently contradictory things about what ends diapause. They were describing different phases. Diapause has an induction, a preparation, a maintenance and a termination phase, followed by a quiescence in which the insect is ready to go and is waiting for warmth — and the insect responds completely differently to the same treatment depending on which one it is in.

Early coverage · 34% complete · reviewed 2026-09-03

What this page covers

Best characterised in insects, where it has been studied across most orders. Comparable anticipatory dormancies occur in mites, crustaceans, some fish and in plant seeds, and are less well described.

Often confused with: Quiescence — a direct response to cold or drought that reverses as soon as conditions improve; Hibernation, which is a response to the season rather than a prediction of it; Simply being too cold to move, which is not a programmed state at all

Quick facts

The cue
Daylength — reliable precisely because it says nothing about current conditions
When it is decided
Before the hardship, sometimes in a previous generation
Cannot be undone by
Warmth, food and long days — the state is programmed, not maintained by conditions
Often ended by
A long period of cold, which the programme requires before it will complete

A prediction, not a response

The cue arrives before the hardship, and carries no information about it.

Diapause is a prediction, not a reaction. It is triggered by daylength before conditions worsen — sometimes a generation ahead — and an insect in diapause moved somewhere warm and well-fed simply stays in diapause.

Established

Specialists would state this without hedging. Multiple independent lines of evidence agree.

Diapause is induced by token environmental cues, predominantly photoperiod, sensed at a species-specific sensitive stage that may precede the diapausing stage by one or more generations. The state is developmentally programmed and is not terminated by the restoration of favourable conditions; termination requires completion of an internal programme, commonly involving prolonged chilling.

Who this applies to
Established in detail across insect orders; comparable anticipatory dormancies occur in some other invertebrates and in plant seeds.
Studied in
Insecta
Why we rate it this way, and what the caveats are
EstablishedHigh confidence

One of the better-established results in insect physiology, replicated across many species and the basis of practical pest forecasting.

How far it can be extended

Photoperiodic induction and refractory termination have been demonstrated independently in many insect orders, though the specific cues and sensitive stages differ by species.

Caveats

  • Responsiveness changes through the phases of diapause, so “cannot be ended by good conditions” holds during maintenance and not during the quiescence that follows termination.
  • Not all insect dormancy is diapause. Quiescence — a direct response to cold or drought that reverses when conditions improve — is common and is frequently mislabelled.

Still unanswered

  • How the photoperiodic timer is implemented molecularly, and how far it shares components with the circadian clock.

Last reviewed 2026-09-03

The evidence (2 studies)

  • Supports · primary

    Regulation of Diapause

    Denlinger, 2002 · Annual Review of Entomology

    The standard review of cue, programme and termination.

  • Supports · supporting

    Eco-physiological phases of insect diapause

    Koštál, 2006 · Journal of Insect Physiology

    Explains why reports about what ends diapause conflict: the animal responds differently in different phases.

The short answer

Why use daylength rather than temperature?

Because temperature lies. A warm week in October says nothing about November, whereas daylength on a given date is identical every year and cannot be misled by weather.

The trade-off is that daylength is a fixed calendar and the climate is not. An insect timing its diapause by daylength gets the same answer every year regardless of how the season is actually running, which was reliable for as long as seasons were. Under a shifting climate this becomes a liability: the cue stays put while the conditions it predicts move, and the mismatch is one of the mechanisms by which warming disrupts insect populations. A more responsive cue would track the change, and would also be fooled by every warm spell.

Check it for yourself

In some species the daylength that determines whether an insect will enter diapause is sensed by its mother, so the decision is made a generation before the animal it applies to exists.

Based on Diapause is a prediction, not a reaction. It is triggered by daylength before conditions worsen — sometimes a generation ahead — and an insect in diapause moved somewhere warm and well-fed simply stays in diapause.

The phases, and why the literature appeared to contradict itself

An insect in diapause responds completely differently to the same treatment depending on when you apply it.

For years, papers disagreed about what ends diapause. Some reported that warmth resumed development; others that it did nothing. Both were right, and the disagreement was about words: diapause is not one state but a sequence, and warmth applied during maintenance does nothing while the same warmth applied after termination starts the insect immediately. Setting out the phases explicitly resolved a confusion that had looked like a conflict of evidence.

The phases, and what the insect will and will not respond to in each
PhaseWhat is happeningResponse to warmth and food
InductionThe cue is sensed and the commitment madeDevelopment continues normally for now
PreparationReserves are laid down, physiology reorganisedStill developing, but the decision is taken
InitiationDevelopment arrestsNone
MaintenanceThe arrest is actively heldNone — this is the phase that surprises people
TerminationThe internal programme completes, often needing coldNone yet, but the block is lifting
Post-diapause quiescenceReady, waiting for conditionsImmediate — development resumes

The last two rows matter for anyone trying to interpret what an insect is doing in spring. An insect that starts developing the moment it warms up may have terminated diapause months earlier and been quiescent all winter. The visible event — movement in spring — is not the end of diapause; it is the end of the waiting that follows it.

Diagram

What the insect responds to, phase by phase

The same treatment produces opposite results depending on when it is applied.

Warmth and food: what the insect does about them, by phaseInductionDevelopsrespondsPreparationDevelopsrespondsInitiationNorespondsMaintenanceNorespondsTerminationNorespondsQuiescenceYesrespondsNothing you do in the middle four phases restarts development.Reports about “what ends diapause” conflicted because they tested different phases.The insect moving in spring often ended diapause months earlier.
The same explanation in words

Six boxes in sequence. During induction and preparation the insect is still developing normally. During initiation, maintenance and termination it does not respond to warmth and food at all. Only in post-diapause quiescence, the sixth box, does it respond — and then immediately. Nothing done during the middle four phases restarts development, which is why published reports about what ends diapause appeared to conflict: they were testing different phases. An insect seen moving in spring has often ended diapause months earlier.

Diapause is not the same as quiescence

The distinction is routinely lost, and it is the difference between a programme and a reaction.

  • Quiescence begins when conditions get bad and ends when they improve. It is immediate, reversible, and requires no advance commitment.
  • Diapause begins before conditions get bad, on a cue unrelated to them, and will not end merely because conditions improve.
  • Much insect dormancy reported as diapause is actually quiescence, because the two look identical from outside — a motionless insect in the cold.
  • The test is straightforward: warm it up. A quiescent insect gets going. A diapausing one does not.

Where diapause fits

A motionless insect in the cold is usually not in diapause. Quiescence — a direct response to bad conditions that reverses as soon as they improve — is commoner, and looks identical from outside.

Established

Specialists would state this without hedging. Multiple independent lines of evidence agree.

Quiescence, an immediate and directly reversible dormancy imposed by unfavourable conditions, is distinct from diapause, which is centrally programmed, photoperiodically induced in advance, and refractory to the restoration of favourable conditions. The two are frequently conflated because they are behaviourally indistinguishable.

Who this applies to
Insects, where both states are well characterised and routinely confused.
Studied in
Insecta
Why we rate it this way, and what the caveats are
EstablishedHigh confidence

The distinction is definitional and operationally testable by a simple manipulation: warm the insect and see whether it resumes development.

How far it can be extended

The distinction is standard across insect physiology and applies wherever both states have been examined.

Caveats

  • An insect can pass through both in one winter — diapause first, then quiescence once the programme has completed — which is why the same animal gives different answers at different times.
  • The test is straightforward in the laboratory and much harder to apply in the field.

Still unanswered

  • What proportion of overwintering insect dormancy reported as diapause is actually quiescence, which has not been surveyed systematically.

Last reviewed 2026-09-03

The evidence (2 studies)

  • Supports · primary

    Eco-physiological phases of insect diapause

    Koštál, 2006 · Journal of Insect Physiology

    Sets out the phases and the terminology, including post-diapause quiescence, which is where the confusion concentrates.

  • Supports · primary

    Regulation of Diapause

    Denlinger, 2002 · Annual Review of Entomology

    Establishes what makes diapause diapause: the token cue and the refractory programme.

The research behind this page

4 studies, newest first. Each one has a page explaining what it found and what it could not show.

2006Journal of Insect Physiology

Eco-physiological phases of insect diapause

Much apparent disagreement in the diapause literature comes from authors using the same word for different phases; separating the phases resolves conflicting reports about what ends diapause.

2004Biological Reviews

Metabolic rate depression in animals: transcriptional and translational controls

Depression is actively controlled rather than passive: the animal shuts most of its gene expression down while keeping a specific protective subset running, and the state is held by modifications that can be reversed quickly.

2002Annual Review of Entomology

Regulation of Diapause

Diapause is a programmed developmental arrest initiated in advance of adverse conditions, not a response to them.

1999Biological Reviews

Metabolic depression in animals: physiological perspectives and biochemical generalizations

Depressed states across very distant phyla converge on a small set of mechanisms — coordinated suppression of protein synthesis and ion pumping, reversible phosphorylation of enzymes, and a general shutdown rather than a targeted one — despite having been named and studied independently.

This page is a stop on a longer route

A guided journey reads several subjects in a deliberate order, with an argument for why one follows another. You can join in the middle.

Where to go from here

Each of these follows from something on this page — a relationship in the evidence, a claim people ask about, or the next mechanism along.

How complete this page is, and what it is still missing

NatureHQ publishes its own gaps. This page is at 34% completeness against what we would call a finished subject, and was last reviewed on 2026-09-03. It carries 3 claims and answers 3 mapped search questions.

  • 1 high-priority search intent(s) not yet covered
  • no research from the last few years is attached — check for newer work
  • more experiments could be explained in plain English
  • no popular claim about this subject has been checked yet
  • The hormonal control of diapause is referred to only in outline.
  • Diapause outside the insects — in mites, crustaceans, killifish and seeds — is mentioned rather than covered.
  • How the photoperiodic timer relates to the circadian clock is an open question that is stated but not explored.