Seasonality of Some Arctic Alaskan Chironomids
Braegelman, Shane Dennis
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Arthropods, especially dipteran insects in the family Chironomidae (non-biting midges), are a primary prey resource for many vertebrate species on Alaska’s Arctic Coastal Plain. Midge-producing ponds on the ACP are experiencing climate warming that may alter insect seasonal availability. Chironomids display highly synchronous adult emergence, with most populations emerging from a given pond within a 3-5 day span and the bulk of the overall midge community emerging over a 3-4 week period. The podonomid midge Trichotanypus alaskensis Brundin is an abundant, univoltine, species in tundra ponds near Barrow, Alaska, with adults appearing early in the annual emergence sequence. To better understand regulation of chironomid emergence phenology, we conducted experiments on pre-emergence development of T. alaskensis at different temperatures, and monitored pre-emergence development of this species under field conditions. We compared chironomid community emergence from ponds at Barrow, Alaska in the 1970s with similar data from 2009-2013 to assess changes in emergence phenology. Overwintering larvae of T. alaskensis increased in larval size, dry weight, and head capsule size between pond thaw and pupation, indicating substantial larval growth as well as development preceding pupation in the year of emergence. Pupal development showed a consistent degree hour requirement independent of mean daily temperature. We detected a significant advancement of overall midge emergence by about one week in Barrow tundra ponds since the late-1970s. Chironomid midge development clearly is regulated by temperature, but at least some species require substantial feeding and growth during the post-thaw period, raising the possibility of nutritional influences on emergence phenology. Under a warming climate, altered adult emergence timing may result from earlier thaw, warmer temperatures, and possible changes in food availability.