Macrobenthos 311 



likely that no feeding or growth occurs during this final season. Instead, as 

 suggested by Danks and Oliver ( 1 972), the final winter diapause serves as a 

 population synchronizing mechanism with prepupal and pupal 

 development filling the time between thawing in mid- to late June and 

 emergence in early to mid-July. Emerging adults flew away from the pond 

 surface and awaited a period of calm or low wind speeds. Males form 

 aerial swarms and females mate and oviposit in the manner described by 

 other authors for most Chironomus species (e.g., Fischer 1969). 



When temperatures begin to fall in late summer, the larvae spin 

 cocoons and then spend the winter frozen solid in the mud (Scholander et 

 al. 1953). The return to activity in June was observed in Chironomus, but 

 this aspect of their biology has been described already by Danks (1971b). 

 The ability to tolerate sub-freezing temperatures may be an important 

 selective factor for the species composition of arctic chironomids (Danks 

 and Oliver 1972). 



Tanytarsus maequalis, a much smaller species also abundant in the 

 pond centers, has a 2-year life cycle. Emergence and oviposition do not 

 take place until late July to early August, yet the newly recruited larvae 

 reach the second instar before overwintering. The molt to the third instar 

 occurs during the second summer, and soon after the second winter the 

 fourth instar is reached. Since these insects will emerge later this same 

 year, it is obvious that much feeding and growth must take place between 

 thawing and emergence. This species, and perhaps others in the Barrow 

 area, do not fit the "absolute spring species" designation of Danks and 

 Oliver (1972) for the midge fauna of a higher arctic location. In such 

 species, no feeding takes place during the summer of emergence. 



The adult behavior of Tanytarsus inaequalis and other small species 

 in these ponds differs from that described for Chironomus pilicornis. 

 Instead of flying away from the pond immediately upon emergence, the 

 adults rest sheltered from the wind among emergent Carex at the pond 

 edges; during periods of calm the males skate over the surface to find 

 mates. This behavior is perhaps best developed in an undescribed sibling 

 species to T. inaequalis, T. gregarius gr. sp. 2. Here, the organs most 

 involved in flight, swarm behavior, and aerial location of a mate are 

 reduced (male antennae, wings) while the genitalia are relatively robust 

 and the abdomen is shorter and wider than in T. inaequalis. Several other 

 sibling species pairs from Barrow include one member with a reduced 

 antennal plume, a phenomenon described as an adaptation to reduced 

 aerial swarming in the windy arctic environment (Wiilker 1959). 



Respiration 



Oxygen uptake rates of Chironomus were measured on groups of 5 to 

 20 larvae in a selected millimeter length class in 6-ml chambers containing 

 Millipore (HA) filtered pond water. Chambers were placed in a water bath 



