Diapause
Encyclopedia
Diapause is the 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 is a mechanism used as a means to survive predictable, unfavorable environmental conditions, such as temperature extremes, drought or reduced food availability. Diapause is most often observed in arthropod
s, especially insect
s, and in the embryo
s of many of the oviparous
species
of fish in the order Cyprinodontiformes
. (Diapause does not occur in embryos of the viviparous
and ovoviviparous
species of Cyprinodontiformes.)
Diapause is not only induced in an organism by specific stimuli or conditions, but once it is initiated, only certain other stimuli are capable of bringing the organism out of diapause. The latter feature is essential in distinguishing diapause as a different phenomenon from other forms of dormancy
such as stratification
, and hibernation
.
Activity levels of diapausing stages can vary considerably among species. Diapause may occur in a completely immobile stage, such as the pupae and eggs, or it may occur in very active stages that undergo extensive migrations, such as the adult Monarch butterfly
, Danaus plexippus. In cases where the insect remains active, feeding is reduced and reproductive development is slowed or halted.
of insects to another, these phases can be characterized by particular sets of metabolic processes and responsiveness of the insect to certain environmental stimuli. Diapause can occur during any stage of development in arthropods, but each species exhibits diapause in specific phases of development. Reduced oxygen consumption is typical as is reduced movement and feeding.
may be altered by changing hydrocarbon
composition and by adding lipids to reduce water loss making the organism resistant to desiccation.
Diapausing pupa
ria 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.
into a specific diapause stage, or be accompanied by color change. Enzymatic
changes may take place in preparation for cold hardening
. For example, only diapausing 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. Insects may also undergo behavioural changes and begin to aggregate, migrate or search for suitable overwinter
ing sites.
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 progresses.
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, for instance in response to warm weather
in late fall. Termination may occur at the height of unfavourable conditions, such as in the middle of winter. Over time, depth of diapause slowly decreases until direct development can resume, if conditions are favourable.
from which the insect can arouse and begin direct development, should conditions change to become more favourable. This allows the insect to continue to withstand harsh conditions while being ready to take advantage of good conditions as rapidly as possible.
al signalling, endocrine pathways and eventually metabolic and enzymatic changes.
. In temperate
regions, photoperiod is the most reliable cues of seasonal change. Depending on the season in which diapause occurs, either short or long days can act as token stimuli. Insects may also respond to changing day length as well as relative day length. Temperature may also act as a regulating factor, either by inducing diapause or, more commonly, by modifying the response of the insect to photoperiod. Insects may respond to thermoperiod, the daily fluctuations of warm and cold that correspond with night and day, as well as to absolute or cumulative temperature. Food availability and quality may also help regulate diapause. In the desert locust
, Schistocerca gregaria, a plant hormone
called gibberellin
stimulates reproductive development. During the dry season, when their food plants are in senescence
and lacking gibberellin, the locusts remain immature and their reproductive tracts do not develop.
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).
Prothoracicotropic hormone 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 prothoracicotropic hormone from the brain or by failure of the prothoracic glands to respond to prothoracicotropic hormone.
The corpora allata is responsible for the production of juvenile hormone
(JH). In the bean bug, Riptortus pedestris, clusters of neurons on the protocerebrum called the pars lateralis maintain reproductive diapause by inhibiting JH production by the corpora allata. Adult diapause is often associated with the absence of JH, while larval diapause is often associated with its presence.
In adults, absence of JH causes degeneration of flight muscles, atrophy
or cessation of development of reproductive tissues, and halts mating behaviour. The presence of JH in larvae may prevent moulting to the next larval instar
, though successive stationary moults may still occur. In the corn borer, Diatraea gradiosella, JH is required for the accumulation by the fat body of a storage protein
that is associated with diapause.
Diapause hormone
regulates embryo
nic diapause in the eggs of the silkworm moth, Bombyx mori. DH is released from the subesophageal ganglion
of the mother and triggers trehalase
production by the ovaries. This generates high levels of glycogen
in the eggs
, which is converted into the polyhydric alcohols glycerol
and sorbitol
. Sorbitol
directly inhibits the development of the embryos. Glycerol
and sorbitol
are reconverted into glycogen
at the termination of diapause.
is often initiated in response to biotic
rather than abiotic factors. For example, food in the form of vertebrate
carcasses may be more abundant following dry seasons, or oviposition
sites in the form of fallen trees may be more available following rainy seasons. Also, diapause may serve to synchronize mating seasons or reduce competition, rather than to avoid unfavourable climatic conditions.
Diapause in the tropics poses several challenges to insects that are not faced in temperate
zones. Insects must reduce their metabolism without the aid of cold temperatures and may be faced with increased water loss due to high temperatures. While cold temperatures inhibit the growth of fungi and bacteria
, diapausing tropical insects still have to deal with these pathogens. Also, predators and parasites
may still be abundant during the diapause period.
Aggregations are common among diapausing tropical insects, especially in the orders Coleoptera, Lepidoptera
and Hemiptera
. Aggregations may be used as protection against predation
, since aggregating species are frequently toxic and predators quickly learn to avoid them. They can also serve to reduce water loss, as seen in the fungus beetle
, Stenotarsus rotundus, which forms aggregations of up to 70,000 individuals, which may be eight beetles deep. Relative humidity
is increased within the aggregations and beetles experience less water loss, probably due to decreased surface area to volume ratios reducing evaporative water loss.
Dormancy
Dormancy is a period in an organism's life cycle when growth, development, and physical activity are temporarily stopped. This minimizes metabolic activity and therefore helps an organism to conserve energy. Dormancy tends to be closely associated with environmental conditions...
with very specific initiating and inhibiting conditions. Diapause is a mechanism used as a means to survive predictable, unfavorable environmental conditions, such as temperature extremes, drought or reduced food availability. Diapause is most often observed in arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
s, especially insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s, and in the embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
s of many of the oviparous
Oviparity
Oviparous animals are animals that lay eggs, with little or no other embryonic development within the mother. This is the reproductive method of most fish, amphibians, reptiles, all birds, the monotremes, and most insects, some molluscs and arachnids....
species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of fish in the order Cyprinodontiformes
Cyprinodontiformes
The Cyprinodontiformes is an order of ray-finned fish, comprising mostly small, fresh-water fish. Many popular aquarium fish, such as killifish and live-bearers, are included. They are closely related to the Atheriniformes and are occasionally included with them...
. (Diapause does not occur in embryos of the viviparous
Vivipary
Vivipary has two different meanings. In animals, it means development of the embryo inside the body of the mother, eventually leading to live birth, as opposed to laying eggs...
and ovoviviparous
Ovoviviparity
Ovoviviparity, ovovivipary, or ovivipary, is a mode of reproduction in animals in which embryos develop inside eggs that are retained within the mother's body until they are ready to hatch...
species of Cyprinodontiformes.)
Diapause is not only induced in an organism by specific stimuli or conditions, but once it is initiated, only certain other stimuli are capable of bringing the organism out of diapause. The latter feature is essential in distinguishing diapause as a different phenomenon from other forms of dormancy
Dormancy
Dormancy is a period in an organism's life cycle when growth, development, and physical activity are temporarily stopped. This minimizes metabolic activity and therefore helps an organism to conserve energy. Dormancy tends to be closely associated with environmental conditions...
such as stratification
Stratification (botany)
In horticulture, stratification is the process of pretreating seeds to simulate natural winter conditions that a seed must endure before germination. Many seed species undergo an embryonic dormancy phase, and generally will not sprout until this dormancy is broken...
, and hibernation
Hibernation
Hibernation is a state of inactivity and metabolic depression in animals, characterized by lower body temperature, slower breathing, and lower metabolic rate. Hibernating animals conserve food, especially during winter when food supplies are limited, tapping energy reserves, body fat, at a slow rate...
.
Activity levels of diapausing stages can vary considerably among species. Diapause may occur in a completely immobile stage, such as the pupae and eggs, or it may occur in very active stages that undergo extensive migrations, such as the adult Monarch butterfly
Monarch butterfly
The Monarch butterfly is a milkweed butterfly , in the family Nymphalidae. It is perhaps the best known of all North American butterflies. Since the 19th century, it has been found in New Zealand, and in Australia since 1871 where it is called the Wanderer...
, Danaus plexippus. In cases where the insect remains active, feeding is reduced and reproductive development is slowed or halted.
Phases of insect diapause
Diapause in insects is a dynamic process consisting of several distinct phases (Kostal 2006). While diapause varies considerably from one taxonTaxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
of insects to another, these phases can be characterized by particular sets of metabolic processes and responsiveness of the insect to certain environmental stimuli. Diapause can occur during any stage of development in arthropods, but each species exhibits diapause in specific phases of development. Reduced oxygen consumption is typical as is reduced movement and feeding.
Comparison of Diapause Periods
The sensitive stage is the period where stimulus must occur to trigger diapause in the organism. Examples of sensitive stage/diapause periods in various insects:- Diatraea grandiosellaSouthwestern corn borerThe southwestern corn borer, Diatraea grandiosella, is a moth belonging to the sub-order Heterocera. Like most moths, The Southwestern corn borer undergoes complete metamorphosis developing as an egg, larva , pupa and adult. It is capable of entering diapause in its larva stage and under the...
(Southwestern corn borer) – sensitive stage: early larva, diapause: late larval - Sarcophaga crassipalpisSarcophaga crassipalpisThe flesh fly Sarcophaga crassipalpis is a common laboratory animal used in the study of gene expression and the study of diapause in insects....
– sensitive stage: early larval, diapause: pupa - Sarcophaga argyrostoma – sensitive stage: mid to late larval, diapause: pupa
- Manduca sexta (Tobacco hornworm) – sensitive stage: late embryonic (egg) to late larval, diapause: pupa
- Lepinotarsa decemlineata – sensitive stage: early adult, diapause: late adult
- Bombyx moriBombyx moriThe silkworm is the larva or caterpillar of the domesticated silkmoth, Bombyx mori . It is an economically important insect, being a primary producer of silk...
(Silkworm) – sensitive stage: late embryonic (egg) to early larval, diapause: embryonic - Lymantria disparGypsy mothThe gypsy moth, Lymantria dispar, is a moth in the family Lymantriidae of Eurasian origin. Originally ranging from Europe to Asia, it was introduced to North America in the late 1860s and has been expanding its range ever since...
(Gypsy moth) – sensitive stage: late embryonic, diapause: late embryonic - Danaus plexipus (Monarch butterfly) – sensitive stage: early adulthood diapause: adulthood
Induction
The induction phase 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, particularly in egg diapause. During this phase, insects are responsive to external cues called token stimuli, which trigger the switch from direct development pathways to diapause pathways. Token stimuli can consist of changes in photoperiod, thermoperiod or allelochemicals from food plants. These stimuli are not in themselves favourable or unfavourable to development, but they herald an impending change in environmental conditions.Preparation
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 fuel for development following diapause termination. Composition of the cuticleCuticle
A cuticle , or cuticula, is a term used for any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticles" are non-homologous; differing in their origin, structure, function, and chemical composition...
may be altered by changing hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....
composition and by adding lipids to reduce water loss making the organism resistant to desiccation.
Diapausing pupa
Pupa
A pupa is the life stage of some insects undergoing transformation. The pupal stage is found only in holometabolous insects, those that undergo a complete metamorphosis, going through four life stages; embryo, larva, pupa and imago...
ria 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.
Initiation
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 moultingEcdysis
Ecdysis is the moulting of the cuticula in many invertebrates. This process of moulting is the defining feature of the clade Ecdysozoa, comprising the arthropods, nematodes, velvet worms, horsehair worms, rotifers, tardigrades and Cephalorhyncha...
into a specific diapause stage, or be accompanied by color change. Enzymatic
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
changes may take place in preparation for cold hardening
Cold hardening
Cold hardening is the physiological and biochemical process by which an organism prepares for cold weather.-Plants:During the winter months, as the leaves fall off deciduous species and the temperature drops, the cold forces a stop to water movement in plants. Freezing water can also cause...
. For example, only diapausing adults of the fire bug, Pyrrhocoris apterus, have the enzymatic complement that allows them to accumulate polyhydric alcohols
Polyol
A polyol is an alcohol containing multiple hydroxyl groups. In two technological disciplines the term "polyol" has a special meaning: food science and polymer chemistry.- Polyols in food science :...
, molecules that help to lower their freezing points and thus avoid freezing. Insects may also undergo behavioural changes and begin to aggregate, migrate or search for suitable overwinter
Overwinter
To overwinter is to pass through or wait out the winter season, or to pass through that period of the year when “winter” conditions make normal activity or even survival difficult or near impossible...
ing sites.
Maintenance
During the maintenance phase, insects experience lowered metabolismMetabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
and developmental arrest is maintained. Sensitivity to certain stimuli which act to prevent termination of diapause, such as photoperiod and temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
, is increased. At this stage, insects are unresponsive to changes in the environment
Natural environment
The natural environment encompasses all living and non-living things occurring naturally on Earth or some region thereof. It is an environment that encompasses the interaction of all living species....
that will eventually trigger the end of diapause, but they grow more sensitive to these stimuli as time progresses.
Termination
In insects that undergo obligate diapause, termination may occur spontaneously, without any external stimuli. In facultative diapausers, token stimuliStimulus (physiology)
In physiology, a stimulus is a detectable change in the internal or external environment. The ability of an organism or organ to respond to external stimuli is called sensitivity....
must occur to terminate diapause. These stimuli
Stimulus (physiology)
In physiology, a stimulus is a detectable change in the internal or external environment. The ability of an organism or organ to respond to external stimuli is called sensitivity....
may include chilling, freezing or contact with water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
, depending on the environmental conditions being avoided. These stimuli
Stimulus (physiology)
In physiology, a stimulus is a detectable change in the internal or external environment. The ability of an organism or organ to respond to external stimuli is called sensitivity....
are important in preventing the insect from terminating diapause too soon, for instance in response to warm weather
Weather
Weather is the state of the atmosphere, to the degree that it is hot or cold, wet or dry, calm or stormy, clear or cloudy. Most weather phenomena occur in the troposphere, just below the stratosphere. Weather refers, generally, to day-to-day temperature and precipitation activity, whereas climate...
in late fall. Termination may occur at the height of unfavourable conditions, such as in the middle of winter. Over time, depth of diapause slowly decreases until direct development can resume, if conditions are favourable.
Post-diapause quiescence
Diapause frequently ends prior to the end of unfavourable conditions and is followed by a state of quiescenceQuiescence
Quiescence may refer to:*Quiescence search, in Game searching in artificial intelligence, a quiescent state is one in which a game is considered stable and unlikely to change drastically the next few plays...
from which the insect can arouse and begin direct development, should conditions change to become more favourable. This allows the insect to continue to withstand harsh conditions while being ready to take advantage of good conditions as rapidly as possible.
Regulation of diapause
Diapause in insects is regulated at several levels. Environmental stimuli interact with genetic pre-programming to affect neuronNeuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
al signalling, endocrine pathways and eventually metabolic and enzymatic changes.
Environmental
Environmental regulators of diapause generally display a characteristic seasonal patternSeason
A season is a division of the year, marked by changes in weather, ecology, and hours of daylight.Seasons result from the yearly revolution of the Earth around the Sun and the tilt of the Earth's axis relative to the plane of revolution...
. In temperate
Temperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...
regions, photoperiod is the most reliable cues of seasonal change. Depending on the season in which diapause occurs, either short or long days can act as token stimuli. Insects may also respond to changing day length as well as relative day length. Temperature may also act as a regulating factor, either by inducing diapause or, more commonly, by modifying the response of the insect to photoperiod. Insects may respond to thermoperiod, the daily fluctuations of warm and cold that correspond with night and day, as well as to absolute or cumulative temperature. Food availability and quality may also help regulate diapause. In the desert locust
Desert locust
Plagues of the desert locust have threatened agricultural production in Africa, the Middle East, and Asia for centuries. The livelihood of at least one-tenth of the world’s human population can be affected by this voracious insect...
, Schistocerca gregaria, a plant hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...
called gibberellin
Gibberellin
Gibberellins are plant hormones that regulate growth and influence various developmental processes, including stem elongation, germination, dormancy, flowering, sex expression, enzyme induction, and leaf and fruit senescence....
stimulates reproductive development. During the dry season, when their food plants are in senescence
Senescence
Senescence or biological aging is the change in the biology of an organism as it ages after its maturity. Such changes range from those affecting its cells and their function to those affecting the whole organism...
and lacking gibberellin, the locusts remain immature and their reproductive tracts do not develop.
Neuroendocrine
The neuroendocrineNeuroendocrinology
Neuroendocrinology is the study of the extensive interactions between the nervous system and the endocrine system, including the biological features of the cells that participate, and how they functionally communicate...
system of insects consists primarily of neurosecretory cells in the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
, the corpora cardiaca, corpora allata and the prothoracic glands. There are several key hormones involved in the regulation of diapause: juvenile hormone
Juvenile hormone
Juvenile hormones are a group of acyclic sesquiterpenoids that regulate many aspects of insect physiology. JHs regulate development, reproduction, diapause, and polyphenisms....
(JH), diapause hormone (DH), and prothoracicotropic hormone
Prothoracicotropic hormone
Prothoracicotropic hormone was the first insect hormone that was discovered. It was originally described simply as "brain hormone" by early workers such as Stefan Kopeć and Vincent Wigglesworth , who realized that ligation of the head of immature insects could prevent molting or pupation of the...
(PTTH).
Prothoracicotropic hormone 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 prothoracicotropic hormone from the brain or by failure of the prothoracic glands to respond to prothoracicotropic hormone.
The corpora allata is responsible for the production of juvenile hormone
Juvenile hormone
Juvenile hormones are a group of acyclic sesquiterpenoids that regulate many aspects of insect physiology. JHs regulate development, reproduction, diapause, and polyphenisms....
(JH). In the bean bug, Riptortus pedestris, clusters of neurons on the protocerebrum called the pars lateralis maintain reproductive diapause by inhibiting JH production by the corpora allata. Adult diapause is often associated with the absence of JH, while larval diapause is often associated with its presence.
In adults, absence of JH causes degeneration of flight muscles, atrophy
Atrophy
Atrophy is the partial or complete wasting away of a part of the body. Causes of atrophy include mutations , poor nourishment, poor circulation, loss of hormonal support, loss of nerve supply to the target organ, disuse or lack of exercise or disease intrinsic to the tissue itself...
or cessation of development of reproductive tissues, and halts mating behaviour. The presence of JH in larvae may prevent moulting to the next larval instar
Instar
An instar is a developmental stage of arthropods, such as insects, between each molt , until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form. Differences between instars can often be seen in altered body proportions, colors, patterns, or...
, though successive stationary moults may still occur. In the corn borer, Diatraea gradiosella, JH is required for the accumulation by the fat body of a storage protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
that is associated with diapause.
Diapause hormone
Hormone
A hormone is a chemical released by a cell or a gland in one part of the body that sends out messages that affect cells in other parts of the organism. Only a small amount of hormone is required to alter cell metabolism. In essence, it is a chemical messenger that transports a signal from one...
regulates embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
nic diapause in the eggs of the silkworm moth, Bombyx mori. DH is released from the subesophageal ganglion
Subesophageal ganglion
The subesophageal ganglion of insects is composed of three pairs of fused ganglia. It controls the mouthparts, the salivary glands and certain muscles....
of the mother and triggers trehalase
Trehalase
Trehalase is a glycoside hydrolase enzyme that catalyzes the conversion of trehalose to glucose. It is found in most animals.The non-reducing disaccharide trehalose is one of the most important storage carbohydrates, which is present in almost all forms of life except mammals...
production by the ovaries. This generates high levels of glycogen
Glycogen
Glycogen is a molecule that serves as the secondary long-term energy storage in animal and fungal cells, with the primary energy stores being held in adipose tissue...
in the eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
, which is converted into the polyhydric alcohols glycerol
Glycerol
Glycerol is a simple polyol compound. It is a colorless, odorless, viscous liquid that is widely used in pharmaceutical formulations. Glycerol has three hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature. The glycerol backbone is central to all lipids...
and sorbitol
Sorbitol
Sorbitol, also known as glucitol, Sorbogem® and Sorbo®, is a sugar alcohol that the human body metabolizes slowly. It can be obtained by reduction of glucose, changing the aldehyde group to a hydroxyl group. Sorbitol is found in apples, pears, peaches, and prunes...
. Sorbitol
Sorbitol
Sorbitol, also known as glucitol, Sorbogem® and Sorbo®, is a sugar alcohol that the human body metabolizes slowly. It can be obtained by reduction of glucose, changing the aldehyde group to a hydroxyl group. Sorbitol is found in apples, pears, peaches, and prunes...
directly inhibits the development of the embryos. Glycerol
Glycerol
Glycerol is a simple polyol compound. It is a colorless, odorless, viscous liquid that is widely used in pharmaceutical formulations. Glycerol has three hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature. The glycerol backbone is central to all lipids...
and sorbitol
Sorbitol
Sorbitol, also known as glucitol, Sorbogem® and Sorbo®, is a sugar alcohol that the human body metabolizes slowly. It can be obtained by reduction of glucose, changing the aldehyde group to a hydroxyl group. Sorbitol is found in apples, pears, peaches, and prunes...
are reconverted into glycogen
Glycogen
Glycogen is a molecule that serves as the secondary long-term energy storage in animal and fungal cells, with the primary energy stores being held in adipose tissue...
at the termination of diapause.
Tropical diapause
Diapause in the tropicsTropics
The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately N and the Tropic of Capricorn in the southern hemisphere at S; these latitudes correspond to the axial tilt of the Earth...
is often initiated in response to biotic
Biotic component
Biotic components are the living things that shape an ecosystem. A biotic factor is any living component that affects another organism, including animals that consume the organism in question, and the living food that the organism consumes. Each biotic factor needs energy to do work and food for...
rather than abiotic factors. For example, food in the form of vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
carcasses may be more abundant following dry seasons, or oviposition
Oviposition
Oviposition is the process of laying eggs by oviparous animals.Some arthropods, for example, lay their eggs with an organ called the ovipositor.Fish , amphibians, reptiles, birds and monetremata also lay eggs....
sites in the form of fallen trees may be more available following rainy seasons. Also, diapause may serve to synchronize mating seasons or reduce competition, rather than to avoid unfavourable climatic conditions.
Diapause in the tropics poses several challenges to insects that are not faced in temperate
Temperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...
zones. Insects must reduce their metabolism without the aid of cold temperatures and may be faced with increased water loss due to high temperatures. While cold temperatures inhibit the growth of fungi and bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
, diapausing tropical insects still have to deal with these pathogens. Also, predators and parasites
Parasitism
Parasitism is a type of symbiotic relationship between organisms of different species where one organism, the parasite, benefits at the expense of the other, the host. Traditionally parasite referred to organisms with lifestages that needed more than one host . These are now called macroparasites...
may still be abundant during the diapause period.
Aggregations are common among diapausing tropical insects, especially in the orders Coleoptera, Lepidoptera
Lepidoptera
Lepidoptera is a large order of insects that includes moths and butterflies . It is one of the most widespread and widely recognizable insect orders in the world, encompassing moths and the three superfamilies of butterflies, skipper butterflies, and moth-butterflies...
and Hemiptera
Hemiptera
Hemiptera is an order of insects most often known as the true bugs , comprising around 50,000–80,000 species of cicadas, aphids, planthoppers, leafhoppers, shield bugs, and others...
. Aggregations may be used as protection against predation
Predation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...
, since aggregating species are frequently toxic and predators quickly learn to avoid them. They can also serve to reduce water loss, as seen in the fungus beetle
Beetle
Coleoptera is an order of insects commonly called beetles. The word "coleoptera" is from the Greek , koleos, "sheath"; and , pteron, "wing", thus "sheathed wing". Coleoptera contains more species than any other order, constituting almost 25% of all known life-forms...
, Stenotarsus rotundus, which forms aggregations of up to 70,000 individuals, which may be eight beetles deep. Relative humidity
Relative humidity
Relative humidity is a term used to describe the amount of water vapor in a mixture of air and water vapor. It is defined as the partial pressure of water vapor in the air-water mixture, given as a percentage of the saturated vapor pressure under those conditions...
is increased within the aggregations and beetles experience less water loss, probably due to decreased surface area to volume ratios reducing evaporative water loss.