This document discusses diapause and hibernation in haematophagous insects. It defines diapause as a period of suspended growth/development in response to adverse conditions, and hibernation as winter dormancy. It provides examples of haematophagous insects that undergo diapause or hibernation, such as certain mosquito species arresting development at the egg stage through desiccation. The document also outlines the physiological processes and environmental/hormonal factors that regulate diapause, such as the role of juvenile hormone and photoperiodism. Genes up/downregulated during mosquito Culex pipiens diapause are also noted.

1. DIAPAUSE & HIBERNATION in
HAEMATOPHAGOUS INSECTS
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2. DIAPAUSE :
HIBERNATION :
HAEMATOPHAGOUS INSECTS :
 A period during which growth or development is suspended and
physiological activity is diminished, as in certain insects in response
to adverse environmental conditions.
 Insects which feeds on blood.
Ex- Mosuito, Sandflies etc.
 It can be expressed as winter dormancy.
 During winter temperature is too cold for ectothermal animals
(including insects) to move around for feeding, thus they undergo
hibernation by reducing the metabolic activity rate.

3.  It can be referred as delay in development in response to regularly and recurring periods of adverse
environmental conditions.
 It is considered to be a physiological state of dormancy with very specific initiating and inhibiting
conditions.
 Diapause may occur in a completely immobile stage, such as the pupae and eggs, or it may occur in
very active stages i.e, In case when insect remains active, feeding reduces or reproductive
development is slow or halted.
 It may occur during any stage of development in arthropods, but each species exhibits diapause in
specific phases of development.
 In some species, the diapause period has become an obligatory part of the life cycle.
 Diapause is facultative and occurs only when induced by certain adverse environmental conditions.
Ex-
DIAPAUSE:
Insect Sensitive phase Diapause
Sarcophaga crassipalpis early larval pupa Pupa
Sarcophaga argyrostoma mid to late larval pupa Pupa

4. TERMINATION PHASE
MAINTENANCE PHASE
INITIATION PHASE
PREPAPRATION PHASE
INDUCTION PHASE

5. Its occurs at a genetically predetermined stage of life and occurs
well in advance of the environmental stress.
This sensitive stage may occur within the lifetime of the diapausing
individual, or in preceding generations i.e, resulting in egg diapause.
During this phase, insects are responsive to external cues called
token stimuli.
Token stimuli can may be any change in photoperiod, thermoperiod,
or allelochemicals from food source.
This triggers the switch from direct development pathways to
diapause pathways.
INDUCTION PHASE

6. The preparation phase usually follows the induction phase.
Though insects may go directly from induction to initiation without a
preparation phase.
During this phase, insects accumulate and store molecules such as
lipids, proteins and carbohydrates.
These molecules are used to maintain the insect throughout diapause
and to provide supplement for development following diapause
termination.
Diapausing puparia of the flesh fly, Sarcophaga crassipalpis increase
the amount of cuticular hydrocarbons lining the puparium, effectively
reducing the ability of water to cross the cuticle.
PREPARATION
PHASE

7. Photoperiod is the most important stimulus initiating diapause.
The initiation phase begins when morphological development ceases.
In some cases, this change may be very distinct and can involve
moulting into a specific diapause stage, or be accompanied by colour
change, behavioural change, migration, aggregation or some
enzymatic change.
Adults of the fire bug, Pyrrhocoris apterus, have the enzymatic
complement that allows them to accumulate polyhydric alcohols,
molecules that help to lower their freezing points and thus avoid
freezing during diapausing.

8. During the maintenance phase, insects experience lowered
metabolism and developmental arrest is maintained.
Sensitivity to certain stimuli which act to prevent termination
of diapause, such as photoperiod and temperature is
increased.
At this stage, insects are unresponsive to changes in the
environment that will eventually trigger the end of diapause,
but they grow more sensitive to these stimuli as time
progress.

9. In insects that undergo obligate diapause, termination may occur
spontaneously, without any external stimuli.
In facultative diapausers, token stimuli must occur to terminate
diapause.
These stimuli may include chilling, freezing or contact with
water, depending on the environmental conditions being
avoided.
These stimuli are important in preventing the insect from
terminating diapause too soon.
The effect of diapause slowly decreases until the insect can
resume its developmental process under favourable condition.

10. REGULATION OF DIAPAUSE :
 It is regulated at several levels.
 Environmental stimuli interact with pre defined genetic pathway to effect
neural signals, endocrine pathways and metabolic and enzymatic changes.
 Environmental regulators of diapause generally display a characteristic
seasonal pattern. Depending upon the season, insect respond to the
photoperiodism and thermoperiodism.
 The neuroendocrine system of insects consists primarily of neurosecretory
cells in the brain, the corpora cardiaca, corpora allata and the prothoracic
glands. There are several key hormones involved in the regulation of
diapause: juvenile hormone (JH), diapause hormone (DH), and
prothoracicotropic hormone(PTTH).
 PTTH stimulates the prothoracic glands to produce ecdysteroids that are
required to promote development. Larval and pupal diapauses are often
regulated by an interruption of this connection, either by preventing release
of PTTH from the brain or by failure of the prothoracic glands to respond to
PTTH. The corpora allata is responsible for the production of JH.

11.  Hibernation refers to period of winter dormancy. Overwintering is a
synonym used for hibernation in insects.
 Hibernation is a behavior in which insects have evolved to survive in
harsh environmental cues.
 In temperate regions, insects undergo hibernation in different life
stages i.e, egg, larval, pupal or adult stage.
 During winter the cold weather can mean that temperatures are too low
for ectothermic animals(insects) for finding food and other resources.
 Insects pass through the winter in every stage of their lives some as
eggs, larvae, pupae, nymphs or as adult.

12.  Hibernation generally includes entry into diapause, a dormant state
that promotes survival by depressing metabolism and energy
utilization under harsh environmental conditions for food and
resources.
 This also includes reduced morphogenesis in immature stages;
hibernating adults typically hibernate before reproducing.
 In polar regions, Production of antifreeze proteins, avoidance of
inoculative freezing by external ice.
 While a few insects are freeze tolerant and can survive the freezing
of 70% or more of their body water.

13. Haematophagous insects :
They feed on humans or animals blood.
Medically important order among insects as haematophagic insects are as
follows:
 Diptera
(includes mosquitoes and flies )
 Anopura
(includes lice)
 Hemiptera
(includes bugs)
 siphnoptera
(includes fleas )

14. DIAPAUSE IN
HAEMATOPHAGOUS INSECTS
 Snow fleas are inactive during summer.
- temperature and humidity are the hatching stimulus
 All species of Aedine genera Aedes, Psorophora and Haemagogus
capable of arresting development at the egg stage.
- they may undergo desiccation up to 1yr or more
- they need to be submerged under water (deoxygenated)
for
hatching (hatching stimulus)
- hatching stimulus is needed for induction and termination
of
diapause (desiccation)
 Aedes triseriatus 4th instar larvae pupate only under constant increased
daylength (i.e, longer day in photoperiodism)
 In culex pipiens, female normally they undergo digest blood meal (trypsin
and a chymotrypsin pathway), as the females then enter diapause,
trypsin and chymotrysin pathway evokes a metabolic switch from blood

15.  In Culex pipiens, there are about 40 genes which are upregulated and
downregulated during diapause, these genes code for functions like regulatory
functions, metabolic functions, digestion, endocrine functions, cytoskeletal
genes, ribosomal genes, transposable elements, and other with unknown
functions.
 Aedes albopictus collection was least during winter in Hanoi, Northern Vietnam
as it undergoes diapause.

16. HIBERNATION IN
HAEMATOPHAGOUS INSECTS
 It mostly occurs in insects living in polar regions.
 Hibernation of Dermacentor marginatus ticks(adult) during august to
september in alpine Armenia.
 Parous Cx. p. pipiens females from region of the northeastern US
enter hibernacula during winter.

17. References :
BOOK :
• Chapman, R.F., (1982) The Insect Structure and Function, Edition 3rd , ELBS
publisher.
• Clements .A.N. (1963) The Physiology of Mosquitoes, pg no: 220-232, The
Macmillian Company, New York.
JOURNALS :
• Tsunoda, T., and et al., Winter Activity and Diapause of Aedes albopictus (Diptera:
Culicidae) in Hanoi, Northern Vietnam., J Med Entomol. (2015)Nov;52(6)
• Mla, R., Hibernation of Dermacentor marginatus ticks in alpine Armenia,
Parazitologiia(1986) NovDec;20(6)
• Robich, R.M., and Delinger, L.D., Diapause in the mosquito Culex pipiens evokes
a metabolic switch from blood feeding to sugar gluttony, PNAS, vol. 104(2005)-44
• Meuti., M. E. and Denlinger., L.D., Evolutionary Links Between Circadian Clocks
and Photoperiodic Diapause in Insects,Int. & Comp. biology(2013)

18. • Denlinger, D.L. and Armbruster., P.A., Mosquito diapause, Annual Review
Entomol.,(2014);59., pg:73-79