Monday, December 10, 2007 - 8:05 AM

Dehydration of the midge, Belgica antarctica: How does an Antarctic insect counter periods of drought?

Joshua B. Benoit, benoit.8@osu.edu1, Giancarlo Lopez-Martinez, lopez-martinez.1@osu.edu1, M. Robert Michaud, michaud.11@osu.edu1, Michael A. Elnitsky, elnitsma@muohio.edu2, Richard E. Lee2, and David L. Denlinger3. (1) Ohio State University, Department of Entomology, 318 West 12th Avenue, Columbus, OH, (2) Miami University, Department of Zoology, 212 Pearson Hall, Oxford, OH, (3) Ohio State University, Entomology, 318 West 12th Avenue, Columbus, OH

During the extended (2 year) development of the Antarctic midge, Belgica antarctica, the larvae are exposed to multiple periods of drying. This study examines physiological responses that reduce stress during desiccation. Based on their high water loss rate (> 10%/h), the larvae are extremely hydrophilic, but this is countered by tolerating the loss of a high percent (>70%) of their water content. Their internal water pool can only be replenished by drinking free water, as evidenced by the fact the larva failed to absorb water from subsaturated water vapor (0.98av). To alleviate dehydration stress, the larvae utilize an array of mechanisms. When held in groups, the larvae suppressed water loss by clustering, which reduced water loss by over 40%. Glycerol increased 2-fold and trehalose increased 3-fold, responses that increase desiccation tolerance and lower water loss rates. The mass of cuticular lipids was not altered in response to dry conditions, but the observed shift to longer hydrocarbons may function in lowering water flux through the cuticle. Drought acclimation permits these larvae to more effectively tolerate subsequent transitions from moist to xeric conditions. Interestingly, exposure of the midge larvae to higher, but still dehydrating, water vapor activities increased dehydration tolerance. In addition, as the larvae dehydrated, their metabolic rate dropped, resulting in a reduction of water loss by respiration. Thus, the midge larvae prevent dehydration by utilizing processes that act to both reduce water loss rate and simultaneously increase desiccation tolerance.

Species 1: Diptera Chironomidae Belgica antarctica (Antarctic midge)