Diapause

In animal dormancy, diapause is the delay in development in response to regular and recurring periods of adverse environmental conditions.

The mechanism is a means of surviving predictable, unfavorable environmental conditions, such as temperature extremes, drought, or reduced food availability.

[17] 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.

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.

These stimuli are important in preventing the insect from terminating diapause too soon, for instance in response to warm weather in late fall.

Environmental stimuli interact with genetic pre-programming to affect neuronal signalling, endocrine pathways, and, eventually, metabolic and enzymatic changes.

[16] This informs entry into reproductive diapause for many northern insects, including the fruit fly Drosophila montana.

Temperature may also act as a regulating factor, either by inducing diapause or, more commonly, by modifying the response of the insect to photoperiod.

[16] 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.

This has been observed in many moth species including the Indian mealmoth, where individuals diapause in different developmental stages due to environmental temperature.

In the desert locust, Schistocerca gregaria, a plant hormone called gibberellin stimulates reproductive development.

[24] 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.

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.

In adults, absence of JH causes degeneration of flight muscles and atrophy or cessation of development of reproductive tissues, and halts mating behaviour.

[27] 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.

Also, diapause may serve to synchronize mating seasons or reduce competition, rather than to avoid unfavourable climatic conditions.