Developmental differences in the sterol composition of Solenopsis invicta

Twenty-six sterols were isolated from eggs, larvae, workers, and queens of the red imported fire ant, Solenopsis invicta Buren. They were identified by chromatographic (TLC, GLC, and HPLC) and spectral methods (MS and 1H-NMR). Queens possessed the most varied sterol composition (24 sterols were detected). The major sterols from queens were the doubly bioalkylated 24 alpha-ethyl cholest-5- and 7-en-3 beta-ols whereas the major sterol from the other developmental stages was cholesterol, a sterol which lacks a C-24 alkyl group. From fourth instar larvae were isolated two yeasts, Candida parapsilosis and Yarrowia lipolytica. Both yeasts were found to synthesize similar sterols, primarily ergosterol and zymosterol (90% of the sterol mixture). A minor sterol (approximately 12% of the total sterol mixture) detected in eggs, larvae, and workers was 24-methyl cholesta-5,22E-dien-3 beta-ol (brassicasterol). Brassicasterol may have originated from ergosterol produced by the fungal endosymbiotes. The amount of sterol in each developmental stage was as follows: approximately 24 microgram sterol/queen, 3 microgram sterol/worker, 2 microgram sterol/larvae, and 0.02 microgram sterol/egg. The sterol composition of the red imported fire ant differed from that of leaf-cutting ants previously investigated where 24-methyl sterols of ectosymbiotic fungal origin were the major sterols detected in soldiers and workers.