Diapause can be defined as the physiological state of dormancy or developmental arrest where most life processes are shut down. It is initiated during unfavourable conditions and is most commonly observed in insects, especially in arthropods.
The diapause stage is can occur at any stage during an insect’s life cycle – from its pupae stage to the active, adult stage. When this phenomenon occurs during the egg or the pupil stage, the development slows down to a halt. In the adult stage, feeding habits or reproductive behaviour is halted or slowed down.
Organisms that Exhibit Diapause
The longest ever diapause to be reported belongs to the Prodoxus Y-inversus, a moth which is found in the United States and South Western New Mexico. It can remain dormant for as long as 19 years.
Diapause during the embryological stage can be observed in many arthropods such as the flesh fly, tobacco hornworm and the Southwestern corn borer.
In fishes, a species called mummichog exhibit diapause during their embryo phase. Even the silkworm exhibits diapause between the late embryonic stage and late larval stage.
Stages of Diapause (Exclusive to insects)
Induction occurs much before the onset of unfavourable environmental conditions. Essentially, certain environmental stimuli, called “token stimuli” triggers the diapause behaviour. The stimuli themselves do not negatively affect any of the factors, though they signify an impending transformation in the environmental conditions.
The induction phase is followed by the preparation phase. This phase is characterized by the insects storing molecules such as carbohydrates, proteins and lipids to sustain themselves during the diapause
One of the most important phases in the stage, the initiation stage is characterized by cessation of morphological development. These include a change in colour, moulting into a diapause stage, or release of special enzymes.
For example, some insects like the firebug accumulate certain chemicals which help in lowering the freezing point.
Maintenance is characterised by the reduced metabolism and arrest of embryological development. Furthermore, sensitivity to certain stimuli is increased, especially the ones that prevent the termination of the diapause is decreased.
Termination, as the name implies, terminates the diapause. However, certain insects rely on specific environmental stimuli to trigger the termination of diapause.
Termination is followed by the state of quiescence, where the insect can resume development, provided the environmental conditions become quite favourable.
Unlike hibernation, diapause does not occur due to the onset of cold weather. Moreover, diapause is predominantly observed in insects and a select group of vertebrates.
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