SEASONAL EMERGENCE OF SOME HIGH ARCTIC CHIRONOMIDAE (DIPTERA)

Abstract

AbstractThe annual emergence of 11 chironomid species from more or less shallow ponds in the area of Hazen Camp (81°49′ N., 71°18′ W.) is considered. Features of emergence are very similar in all these arctic species, although different species emerge at slightly different times in the same habitat.In the deeper habitats, emergence from a deep site is slightly later than that from a shallower one in the same pond. There are very marked differences in times of emergence from pond to pond: emergence of 50% of the annual total for a given species may be reached in different ponds up to 3 weeks apart. These differences from habitat to habitat mean that adults are present over the general Hazen area throughout the arctic summer.The time at which emergence begins in a given pond (or given site within a deeper pond) is primarily dictated by the temperature required for pre-emergence development, but also by other features of individual ponds. Pond temperatures near 4° or 5 °C are most important in this respect. The time of first emergence differs between years in the same pond according to year-to-year temperature differences.Emergence of a given species is basically highly synchronized within a pond, but the emergence period may be prolonged by lowered temperatures acting as a threshold for adult emergence at about 7 °C. The emergence pattern is less regular in shallow ponds in which the temperature fluctuates greatly, and it is more regular with lower peaks in deeper ponds.Males of a number of species generally emerge slightly before the females.Emergence of given species within given ponds is synchronized because only larvae which are ready to pupate without further feeding in spring emerge in any year. There must therefore be control of a ’diapause’ type.Aquatic insect species are characterized as ’absolute spring species’ if all potential émergents overwinter as mature larvae (i.e. larvae in which no further growth is necessary before emergence) and also ’diapause’ is present at this stage. To this category all of these high arctic species belong. They are apparently derived from ’absolute spring species’ farther south, the life-cycles of which are pre-adapted to the shortness of the arctic season. Despite the potential for highly synchronized emergence which such species possess, this potential is not fully realized in the arctic because the irregular fluctuations of temperature there operate near values which may directly inhibit development and emergence.