POLYUNSATURATED FATTY-ACIDS IN NEUTRAL LIPIDS AND PHOSPHOLIPIDS OF SOME FRESH-WATER INSECTS

The fatty acid compositions of total neutral lipids and total polar li pids from eight species of freshwater insects were determined: stonefl y nymphs (Plecoptera), beetle larvae (Coleoptera), Chironomidae (Dipte ra), water boatmen (Corixidae and Notonecta; Heteroptera) and mayfly n ymphs (Ecdyonurus venosus, Caenis, Ephemerella; Ephemeroptera). In add ition, the compositions of individual phosphoglycerides were determine d for four of the species (Plecoptera, Corixidae, Ecdyonurus venosus a nd Emphemerella). Saturated and monounsaturated fatty acids together r epresented up to 85% of the fatty acids of total neutral lipids with 1 6:0 (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 monoun saturates, 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. A rachidonic acid, 20:4n-6 (0.4-1.0%) and 22:6n-3 were, respectively, mi nor and insignificant components of total neutral lipids. PUFA were ma jor fatty acids (34-56% of the total) in total polar lipids and in pho sphatidylcholine, phosphatidylethanolamine, phosphatidylserine and pho sphatidylinositol. The major PUFA present were 20:5n-3 (14-27%) and 18 :3n-3 (6-23%). The most abundant n-6 PUFA, especially in phosphoglycer ides from Corixidae, was 18:2n-6 (3-11%). Arachidonic acid, 20:4n-6, w as present in all phosphoglycerides accounting for 1-4% of the total f atty acids, except in the phosphatidylinositol of Corixidae where it a ccounted for 12% of the total. 22:6(n-3) was not present in significan t 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, es pecially in phosphatidylethanolamine. 16:0 was abundant in phosphatidy lcholine (11-21%), and 18:0 (17-23%) was abundant in phosphatidylserin e. The results are discussed in relation to the functions and origins of PUFA in freshwater insects.