Journal of Insect Physiology 53 (2007) 656–667 Mechanisms to reduce dehydration stress in larvae of the Antarctic midge, Belgica antarctica Joshua B. Benoit a,Ã , Giancarlo Lopez-Martinez a , M. Robert Michaud a , Michael A. Elnitsky b , Richard E. Lee Jr b , David L. Denlinger a a Department of Entomology, The Ohio State University, 318 W. 12th Avenue, Columbus, OH 43210, USA b Department of Zoology, Miami University, Oxford, OH 45056, USA Received 26 January 2007; received in revised form 16 April 2007; accepted 17 April 2007 Abstract The Antarctic midge, Belgica antarctica, is exposed to frequent periods of dehydration during its prolonged larval development in the cold and dry Antarctic environment. In this study, we determined the water requirements of the larvae and the mechanisms it exploits to reduce the stress of drying. Larvae lost water at an exceptionally high rate (410%/h) and tolerated losing a high portion (470%) of their water content. Larvae were unable to absorb water from subsaturated water vapor (p0.98 a v ) to replenish their water stores, thus this midge relies exclusively on the intake of liquid water to increase its pool of body water and maintain water balance. To reduce dehydration stress, the midge employed a variety of mechanisms. Behaviorally, the larvae suppressed water loss by clustering. In response to slow dehydration, glycerol concentration increased 2-fold and trehalose concentration increased 3-fold, responses that are known to decrease the rate of water loss and increase dehydration tolerance. No changes in the mass of cuticular lipids occurred in response to desiccation, but the observed shift to longer hydrocarbons likely contributes to reduced water loss as the larvae dehydrate. As the larvae dehydrated, their oxygen consumption rate dropped, resulting in a reduction of water loss by respiration. Lastly, one bout of slow dehydration also enhanced the larva’s ability to survive subsequent dehydration, suggesting that the larvae have the capacity for drought acclimation. Thus, these hydrophilic midge larvae prevent dehydration by multiple mechanisms that collectively reduce the water loss rate and increase dehydration tolerance. r 2007 Elsevier Ltd. All rights reserved. Keywords: Water balance; Chironomid; Dehydration resistance; Drought acclimation; Antarctica 1. Introduction The habitat range of the Antarctic midge, Belgica antarctica, extends along the west coast of the Antarctic Peninsula with sporadic, but highly dense, populations in localized areas (Usher and Edwards, 1984; Sugg et al., 1983). During its 2-year life cycle, larvae feed on moss, terrestrial algae and other types of organic debris (Convey and Block, 1996; Sugg et al., 1983). All four larval instars are capable of overwintering. The adults emerge, mate, lay eggs and die with a 10–14 d period during the austral summer. During most of the year, the larvae are frozen in their hibernacula, buffered at 0 to 5 1C by thick snow and ice cover (Baust and Lee, 1981; Lee et al., 2006). While frozen, the midge larvae are in vapor pressure equilibrium with the local environment, and no dehydration can occur (Holmstrup et al., 2002a, b; Lee et al., 2006). Even when not frozen, the highly permeable larvae likely are very close to vapor pressure equilibrium due to their relatively high osmolality (Lee et al., 2006; Hayward et al., 2007). Thus, with their high permeability, the midges will likely dehydrate and rehydrate in response to minor changes in the immediate habitat and continually maintain vapor pressure equilibrium, as described by Holmstrup et al. (2002a) for Collembola. Interestingly, the high permeabil- ity that allows larvae of B. antarctica to obtain vapor pressure equilibrium during most of the year is a severe ARTICLE IN PRESS www.elsevier.com/locate/jinsphys 0022-1910/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jinsphys.2007.04.006 Ã Corresponding author. Tel.: +1 614 247 5093; fax: +1 614 292 2180. E-mail address: benoit.8@osu.edu (J.B. Benoit).