Internal lipids of sugarbeet root maggot (Tetanops myopaeformis) larvae: effects of multi-year cold storage.

ABSTRACT

Sugarbeet root maggots, Tetanops myopaeformis (Diptera, Ulidiidae), survive more than five years of laboratory cold (6 degrees C) 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 (161) was the predominant FA, constituting 40-50% of total unsaturated FAs with lesser amounts of myristoleic (141), oleic (181), lauroleic (121), gadoleic (201), and the saturated FAs, palmitic (160), myristic (140), lauric (120), stearic (180), and arachidic (200) 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, TAGs 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.