Graduate Thesis Or Dissertation
 

Essential fatty acids in noctuid moths : their nutrition and metabolism

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  • The polyunsaturated fatty acids (PUFA) are known to be required for larval growth and normal wing development in several species of Lepidoptera but most of the basic information necessary for a complete understanding of this nutritional phenomenon has not been gathered. This includes the role of each of the essential fatty acids, the dietary level for normal development, the effect of age, sex, stage of development, and rearing conditions, fatty acid levels of insect tissues under normal and deficiency conditions, the biochemical distribution of the essential nutrients, and the biochemical fate of these critical constituents. The purpose of this research was to collect such information for linoleic acid (18:2) and linolenic acid (18:3) in three Noctuidae. Trichoplusia ni (Hubner), Autographa californica (Speyer) and Heliothis zea (Boddie) were reared on artificial diets which were supplemented with vegetable oils or individual fatty acids as the only lipid sources. Pupae were reared to adult eclosion at either 23 or 30°C and relative humidities ranging from 20 to 95%. Nutritional adequacy of diets was assessed by larval growth rates, percentage of pupation, and the degree of wing deformity. Gas and thin-layer chromatography were used for fatty acid analyses of the total lipids and lipid classes of pupae from the various nutritional and environmental conditions. Radioactive linolenic acid was used to follow the metabolic fate of this essential fatty acid (EFA). Under standard dietary conditions the PUFA accounted for a greater portion of the fatty acids in the phospholipids (PL) than in the triglycerides (TG) of T. ni larvae, pupae, and adults. There was little change in the component fatty acids when pupae developed at a constant temperature and humidity and no sexual dimorphism in lipid content was detected. The higher temperature and both humidity extremes acted as stress factors affecting wing condition, apparently at the time of eclosion and wing expansion, in insects reared on marginal levels of dietary EFA. With adequate EFA these stresses were overcome. The 18:3 content of total fatty acids, PL, and TG was not different in T. ni and H. zea reared at the two temperatures. Linolenate was verified as the sole EFA for normal wings in T. ni, and A. californica was found to have the same qualitative specificity. H. zea was found to utilize either 18:2 or 18:3 for normal wings, although the latter was more than three times as effective. There was no EFA activity by an EFA analog and several homologous PUFA although they were incorporated into the tissue lipids. Minimal levels of dietary 18:3 for normal wings ranged from 0.05 to 0.25%, depending on the species. The 18:3 necessary for normal wings could be supplied by feeding larvae an adequate diet one day prior to pupation or it could be depleted by feeding such larvae on 18:3 deficient diet. The absence of dietary PUFA resulted in abnormally high amounts of monoenoic acids in the tissue lipids. Tissue levels of PUFA increased as their dietary levels increased, resulting in decreased monoene content. The saturated fatty acids were practically unaffected. A majority of the ¹⁴C-18:3 consumed by the larvae was unaltered and was located in the phospholipids and triglycerides. Suboptimal dietary levels or short-term exposure to dietary 18:3 resulted in most of this EFA being incorporated into the phospholipids. Sustained feeding at above optimum levels eventually resulted in a greater quantity of 18:3 in the TG. Phosphatidylcholine and phosphatidylethanolamine contained approximately 65% of the PL 18:3 regardless of the dietary level or feeding period.
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