The Larvae of the Biggest Antarctic Insect Have an Unusual Physiology

The antarctic midge (Belgica antarctica) is also the only insect and the largest free-roaming terrestrial animal known to inhabit Antarctica, even if it is as big as a rice grain. "It's the largest species that has adapted to living on the continent year-round," said Denlinger, adding that other native animals - such as seals and penguins - spend much of their time in the water.

The midges live in penguin colonies, where they feed on algae and waste material. Scientists have found that the larvae of this species, resembling tiny black worms, produce heat-shock proteins during all their existence, while the adults produce this protein only in case of extreme heat stress, like most animals, including mammals. "The proteins help defend the larval midges against environmental stresses including temperature changes as well as changes in water, oxygen and pH levels," said David Denlinger, professor of entomology at Ohio State University.

"They've somehow figured out a way to maintain a level of these heat-shock, or stress, proteins and still make proteins that are vital for growth and development," he said.

This mechanism seen on the midges larvae offers protection during their two-year life span, most of which is spent encased in ice. "Yet when most insects express stress proteins, it temporarily compromises the production of other proteins," Denlinger said.

"The production of stress proteins usually brings development to a halt," he said.

"But in this case, the larvae merrily go about their business of feeding and growing while producing their stress proteins."

Penguins colonies along the Antarctic coast, which form the habitat of the midges, have an average summertime temperature of around 36�F (2�C). The researchers exposed the larvae and adults to 39.2�F (4�C) and to 68�F (20�C). They wanted to see if the larval and adult midges showed any resilience against the higher temperature. Adult Antarctic midges live one to two weeks in the field and - in the laboratory - the adults lived for five to six days at the lower temperature, but exposed to the higher temperature died in less than a day. However, the larval midges lived up to four days at the higher temperature - four times longer than the adults. "The adults were considerably less heat-tolerant than the larvae," Denlinger said.

"The larval midges continuously express heat-shock proteins and are therefore prepared to respond to the normal kinds of challenges that they face in the harsh Antarctic environment. But the adults produce these proteins only when directly confronted with an environmental challenge."

"Clearly there is some kind of developmental switch that happens between the larval stage and adulthood," he added. "We're just not sure what that is."

Now the researchers want to study the larvae during the long Antarctic winter, when they are encased in ice for months. Even if not active during winter, many insects respond to changes in day length, which regulate their development.

This study could help the world of science to get an insight on the nature and role of heat-shock proteins.