DIAPAUSE & HIBERNATION in

HAEMATOPHAGOUS INSECTS by;

Anil kumarMPHE 1st year(2015-2017)

103

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.

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 DiapauseSarcophaga crassipalpis

early larval pupa Pupa

Sarcophaga argyrostoma

mid to late larval pupa Pupa

DIAPAUSE :

TERMINATION PHASE

MAINTENANCE PHASE

INITIATION PHASE

PREPAPRATION PHASE

INDUCTION PHASE

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

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 increasethe amount of cuticular hydrocarbons lining the puparium, effectively reducing the ability of water to cross the cuticle.

PREPARATION PHASE

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.

INITIATION PHASE

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.

MAINTENANCE PHASE

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.

TERMINATION PHASE

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.

HIBERNATION 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.

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.

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 )

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 feeding to sugar gluttony. At the time of reactivation(about 18°c) at favorable condition it again slowly switches its pathway to trypsin and chymotrypsin.

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.

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.

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)

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