Survival of Heleomyza borealis (Diptera, Heleomyzidae) larvae down to − 60°C
Summary Heleomyza borealis Boh. (Diptera, Heleomyzidae) overwinters as larvae in Arctic habitats, where they may experience winter temperatures below − 15°C. The larvae freeze at c. − 7°C but in acclimation experiments 80% survived when exposed to − 60°C. Of the larvae exposed to between − 4 and − 1...
| Published in: | Physiological Entomology |
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| Main Authors: | , , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
Wiley
2000
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| Subjects: | |
| Online Access: | http://dx.doi.org/10.1046/j.1365-3032.2000.00159.x https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1046%2Fj.1365-3032.2000.00159.x http://onlinelibrary.wiley.com/wol1/doi/10.1046/j.1365-3032.2000.00159.x/fullpdf |
| Summary: | Summary Heleomyza borealis Boh. (Diptera, Heleomyzidae) overwinters as larvae in Arctic habitats, where they may experience winter temperatures below − 15°C. The larvae freeze at c. − 7°C but in acclimation experiments 80% survived when exposed to − 60°C. Of the larvae exposed to between − 4 and − 15°C, only 3% pupated. However, when cooled to − 20°C this increased to 44%, with 4% emerging as adults. Larvae maintained at 5°C contained low levels of glycerol, sorbitol and trehalose, which did not increase with acclimation to low temperatures. However, levels of fructose increased from 6.1 μg mg −1 fw in control animals to 17 μg mg −1 fw when exposed to − 2°C for 1 week. Larval body water (2.2 ± 0.1 g/g dw, mean ± SD, n = 100) and lipid content (0.22 ± 0.002 g/g fw, mean ± SE) showed no significant change during acclimation to low temperatures. Larvae maintained at a constant 5°C survived for over 18 months with little loss of body mass (from 7.5 ± 1.2 to 7.0 ± 1.2 mg fw, mean ± SD, n = 20), but none pupated. Heleomyza borealis larvae appear to feed and grow until they reach a body mass of about 7.5 mg and then become dormant. They remain in this state until they experience a low temperature stimulus (< − 15°C) followed by a warm period (≈ 5°C). This ensures that the larvae pupate and adults emerge in early summer, allowing the maximum growing period before the following winter. Heleomyza borealis are adapted to survive long winters in a dormant larval state. They have a low metabolic rate, can conserve body water even at subzero temperatures but do not synthesize large quantities of cryoprotectants. |
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