The de novo biosynthesis of 5,11,14-eicosatrienoic acid (5,11,14-20:3), arachidonic acid (20:4( n−6)) and eicosadienoic acid (20:2( n−6)) and the elongation/desaturation of linoleic acid (18:2( n−6)) to 20:4( n −6) and α-linolenic acid (18:3( n−3)) to eicosapentaenoic acid (20:5( n−3)) were demonstrated in adult males of the field cricket Teleogryllus commodus. Sodium [1- 14C]acetate, [1- 14C]18:2( n−6) and [1- 14C]18:3( n−3) were injected into adult male crickets and after an incubation period, the testes and remaining tissues were extracted and the methyl esters obtained from the phospholipid and triacylglycerol fractions were analyzed. After 5 days of daily injections of [1- 14C]acetate, the methyl esters of the triene and tetraene fatty acids from the testicular phospholipid fraction were purified by AgNO 3-TLC and HPLC and analyzed by GLC, radio-HPLC, and radio-GLC of ozonolysis products. The results demonstrate the de novo biosynthesis of 20:2( n−6), 20:4( n−6) and an isomer of 20:3( n−6) with double bonds in the 5,11,14 positions. The elongation/desaturation of 18:2( n−6) to 20:4( n−6) and 18:3( n−3) to 20:5( n−3) was demonstrated by analysis of the methyl esters derived from the testicular phospholipid fraction by radio-HPLC after injecting crickets with radiolabeled substrates.