Fatty Acids Differ Significantly in Castes of the Formosan Subterranean Termite (Isoptera: Rhinotermitidae)

Abstract

Identification and quantitation of fatty acids (FAs) in nymphs, alates, workers, presoldiers, and soldiers of the Formosan subterranean termite, Coptotermes formosanus Shiraki, were determined by gas chromatography–mass spectrometry, showing quantitative and qualitative differences among groups. Total FAs content of nymphs and alate females was about 1.5-fold higher than alate males, about 2-fold higher than workers, 6-fold higher than presoldiers, and 12-fold higher than soldiers. Overall differences in total FAs content were due to oleic acid (C18:1), stearic acid (C18:0), linoleic acid (C18:2), and palmitic acid (C16:0). Soldiers contained two unique FAs among the castes—lignoceric (C24:0) and hexacosanoic acid (C26:0). Nymphs had the highest ratio between triacylglycerols and phospholipids probably for energy storage in alate development. Four branched FAs—13-methyl myristic, 14-methyl pentadecenoic, 15-methyl palmitic, and 14-methyl palmitic—and three odd-numbered FAs—pentadecanoic (C15:0), heptadecanoic (C17:0), and heptadecenoic (C17:1)—were found in nymphs, alates, workers, presoldiers, and soldiers. Interestingly, all FAs were distributed in different percentages both in triglycerides and phospholipids of the different developmental stages and castes, indicating a function both for energy storage and membrane components. Five different 2-hydroxy FAs—2-OH C16:0, 2-OH C18:0, 2-OH C20:0, 2-OH C22:0, and 2-OH C24:0—were identified, the latter only in soldiers. Total 2-hydroxy FAs content in soldiers was significantly higher than that in other groups (6.01–7.9-fold vs. presoldiers and 41.7–132.6-fold vs. nymphs, alates, and workers), and the quantity in presoldiers was significantly higher than in nymphs, alates, and workers, with no difference among nymphs, alates, and workers.