Seasonal changes in fatty acid composition associated with cold-hardening in third instar larvae of Eurosta solidaginis |
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Authors: | Valerie A Bennett Nancy L Pruitt Richard E Lee Jr |
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Institution: | (1) Department of Biology, Colgate University, Hamilton, NY 13346, USA Tel: +1-315/824-7398, Fax: +1-315/824-7997 e-mail: npruitt@center.colgate.edu, US;(2) Department of Zoology, Miami University, Oxford, OH 45056, USA, US |
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Abstract: | Third-instar larvae of the goldenrod gall fly Eurosta solidaginis (Diptera: Tephritidae) survive extended periods in winter during which tissue water is frozen. Both low temperature and reduced
water activity during freezing present challenges for the structural integrity of cellular lipids. Fatty acids of both phospholipids
and triacylglycerols from fat body cells of E. solidaginis were analyzed throughout fall and early winter, a period that encompasses the acquisition of freeze-tolerance, to determine
if adaptations to freezing include changes in fatty acid unsaturation. The five most abundant fatty acids from both fractions
were (in decreasing order) oleic (40–65%), palmitoleic (18–20%), palmitic (12–17%), linoleic (5–10%), and stearic acids (4 –7%).
This represents a typical complement of Dipteran fatty acids, although oleic acid levels were higher in E. solidaginis than those reported from other Dipterans (˜28%; Downer 1985). From September to November, monounsaturates increased from
59 to 70% in phospholipids at the expense of saturated fatty acids (25% –20%) suggesting activation of a Δ9-desaturase enzyme. These changes resulted in an increase in the ratio of unsaturated to saturated fatty acids (U/S) from
3.0 to 4.2, although there was no change in the average number of double bonds per fatty acid (unsaturation index, UI ≈ 1.2
in phospholipids and 0.9 in triacylglycerols throughout the season). These changes were temporally correlated to decreasing
ambient temperatures and increasing larval and fat body cell freeze-tolerance.
Accepted: 31 October 1996 |
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Keywords: | Eurosta solidaginis Insect cold-hardiness Homeoviscous adaptation Lipid composition Fatty acid composition |
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