Diapause

Diapause is a programmed pause in development that allows an animal, mainly an insect, to survive a period of unfavorable conditions such as winter or drought. Unlike simple cold-induced torpor, diapause is triggered in advance by cues like day length and continues for a set period even if conditions improve.

The most common cue is the shortening of the day in autumn, which is detected by the brain. Hormones then change the course of development: in many insects falling levels of juvenile hormone or ecdysone halt growth. Metabolism drops sharply, cold tolerance increases, and fat is stored. Diapause can occur in eggs, larvae, pupae or adults, depending on the species, and it is a form of phenotypic plasticity.

The eggs of the Asian tiger mosquito, Aedes albopictus, in temperate regions enter diapause when the mother experiences short days, which lets the species survive winters in the northern United States and Europe. Some Culex pipiens females overwinter as diapausing adults. The migratory monarch butterfly delays reproduction during its journey to Mexico, and silkworm eggs enter diapause controlled by a maternal hormone. Embryonic diapause also occurs in some mammals, such as the red kangaroo and the grizzly bear.

Diapause allows pests and disease vectors to survive winters, affecting where mosquito-borne diseases can persist, and it is therefore a focus of vector control. It also makes insects sensitive to climate change, because the timing set by day length may no longer match the temperature. Many ectotherms rely on it.

• Aedes albopictus — a mosquito with egg diapause
• Monarch Butterfly — a species with reproductive diapause
• Phenotypic Plasticity — the wider concept