Submitted to: Comparative Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2010
Publication Date: 9/1/2010
Publication URL: ddr.nal.usda.gov/bitstream/10113/43910/1/IND44405008.pdf
Citation: Chirumamilla, A., Buckner, J.S., Yocum, G.D., Fatland, C.L., Boetel, M.A. 2010. Internal Lipids of Sugarbeet Root Maggot (Tetanops myopaeformis) Larvae: Effects of Multi-year Cold Storage. Comparative Biochemistry and Physiology B. 157(1):73-79 Interpretive Summary: Diapause and quiescence are frequently encountered phenomena in most insects inhabiting temperate climates. Although diapausing and quiescent insects share a common feature of maintaining low metabolic activity, the cost of extended dormancy periods can draw heavily on energy reserves. Lipids play an important role in energy supply and storage during insect diapause. The sugarbeet root maggot, Tetanops myopaeformis (Röder), is a significant economic pest in the sugarbeet growing areas of North Dakota and Minnesota that overwinters as a mature third-instar larva. This freeze tolerant insect is also known for its remarkable ability to survive long-term (5 years) laboratory storage at 6oC either in a state of post-diapause quiescence or prolonged diapause. In the present study, internal lipids of long-term stored larvae were compared with those of field-collected diapausing larvae to determine energy costs associated with prolonged storage and to characterize lipid usage patterns during the storage period. In addition, fatty acid composition was assessed in diapausing and stored larvae (i.e., 1-, 2-, and 5-year), to determine if long-term storage impacts the distribution or composition of fatty acids in T. myopaeformis larvae. Internal lipid concentration, was highest (21.8% wet wt. and 29.8% dry wt., respectively) in diapausing larvae and decreased progressively over storage time with greater than 70% reductions for 5-year stored larvae. Triacylglycerols (TAG) were the most predominant class of internal lipids and gas chromatography-mass spectrometry (GC-MS) analyses of TAG fractions identified ten major fatty acids (FAs). The proportion of unsaturated FAs was higher (73 to 78%) than saturated FAs in diapausing and stored larval groups. Palmitoleic acid was the predominant FA, constituting 40-50% of total unsaturated FAs. The percentage composition and distribution of individual TAGs remained considerably similar in both the larval groups with even-carbon number fatty acid chain lengths (C42 – C52). In conclusion, it is clear that the insect can use lipids as key energy sources in a gradual pattern over time to sustain itself through diapause and long-term survival and that the long-term storage has no impact on the composition and distribution of fatty acids.
Technical Abstract: Sugarbeet root maggots, Tetanops myopaeformis (Röder), survive more than five years of laboratory cold (6oC) storage as mature third-instar larvae. To quantify energy costs associated with prolonged storage, internal lipids of larvae stored for 1, 2, 3, and 5 years were compared and characterized with those of field-collected diapausing larvae. Internal lipid concentration was highest (21.8% wet wt. and 29.8% dry wt.) in diapausing larvae. Lipids decreased progressively over storage time with greater than 70% reductions for 5-year stored larvae. Thin-layer chromatographic analysis revealed that triacylglycerols (TAGs) were the most predominant class of internal lipids, with trace amounts of diacylglycerols and hydrocarbons also being present. Gas chromatography-mass spectrometry (GC-MS) analyses of TAG fractions identified ten major fatty acids (FAs). The proportion of unsaturated FAs was higher (73 to 78%) than saturated FAs in diapausing and stored larval groups. Palmitoleic acid (16:1) was the predominant FA, constituting 40-50% of total unsaturated FAs with lesser amounts of myristoleic (14:1), oleic (18:1), lauroleic (12:1), gadoleic (20:1), and the saturated FAs, palmitic (16:0), myristic (14:0), lauric (12:0), stearic (18:0), and arachidic (20:0) being detected at much lower concentrations. Characterization of intact TAGs by high performance liquid chromatography and GC-MS revealed the presence of more than 40 TAG constituents. In conclusion, lipids are utilized as an important energy source for T.myopaeformis larvae during diapause and long-term cold storage with no observed impact of multi-year storage on the TAG composition and distribution of their fatty acids.