Polyunsaturated fatty acids in neutral lipids and phospholipids of some freshwater insects

The fatty acid compositions of total neutral lipids and total polar lipids from eight species of freshwater insects were determined: stonefly nymphs (Plecoptera), beetle larvae (Coleoptera), Chironomidae (Diptera), water boatmen (Corixidae and Notonecta; Heteroptera) and mayfly nymphs (Ecdyonurus venosus, Caenis, Ephemerella; Ephemeroptera). In addition, the compositions of individual phosphoglycerides were determined for four of the species (Plecoptera, Corixidae, Ecdyonurus venosus and Emphemerella). Saturated and monounsaturated fatty acids together represented up to 85% of the fatty acids of total neutral lipids with 16:0 (18-31%) being the most abundant saturated fatty acid and 16:1n-7 (10-28%), 18:1n-9 (6-12%) and 18:1n-7 (3-12%) the most abundant monounsaturates, Polyunsaturated fatty acids (PUFA) accounted for between 16% and 33% of the total fatty acids of neutral lipids, with 20:5n-3 (4-12%), 18:3n-3 (3-30%) and 18:2n-6 (1-8%) all being major components. Arachidonic acid, 20:4n-6 (0.4-1.0%) and 22:6n-3 were, respectively, minor and insignificant components of total neutral lipids. PUFA were major fatty acids (34-56% of the total) in total polar lipids and in phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine and phosphatidylinositol. The major PUFA present were 20:5n-3 (14-27%) and 18:3n-3 (6-23%). The most abundant n-6 PUFA, especially in phosphoglycerides from Corixidae, was 18:2n-6 (3-11%). Arachidonic acid, 20:4n-6, was present in all phosphoglycerides accounting for 1-4% of the total fatty acids, except in the phosphatidylinositol of Corixidae where it accounted for 12% of the total. 22:6(n-3) was not present in significant amounts in any phosphoglyceride in any species. 18:1n-9 (8-20%) and 18:1n-7 (2-14%) were the most abundant monounsaturated fatty acids, especially in phosphatidylethanolamine. 16:0 was abundant in phosphatidylcholine (11-21%), and 18:0 (17-23%) was abundant in phosphatidylserine. The results are discussed in relation to the functions and origins of PUFA in freshwater insects.