Chemical composition of cornicle secretion of the brown citrus aphid Toxoptera citricida
2016
Alfaress, Serine | Hijaz, Faraj | Killiny, Nabil
Brown citrus aphid Toxoptera citricida Kirkadly is considered as an important pest of citrus because it vectors citrus tristeza closterovirus. Aphids secrete a fluid from their cornicles as a defensive mechanism against natural enemies. Earlier studies on cornicle secretions of aphids focus only on triglycerides and fatty acids. In the present study, three different methods are used to investigate the chemical composition of the cornicle fluid of T. citricida. Gas chromatography with flame ionization detection is used to detect and quantify the triglycerides after trimethylsilyl derivatization, and gas chromatography‐mass spectrometry (GC‐MS) is used to determine the fatty acid composition after derivatization with boron trifluoride–methanol. Other compounds are detected using GC‐MS after methoxyamine hydrochloride and N‐methyl‐N‐(trimethylsilyl)trifluoroacetamide derivatization. The major fatty acid in the cornicle secretion of T. citricida is palmitic acid. Oleic, stearic, myristic, myristoleic and sorbic acids are also detected, although in low amounts. Sorboyl, dipalmitoyl (C₆ ‐₂, C₁₆, C₁₆) and disorboyl, stearoyl (C₆ ‐₂, C₆ ‐₂, C₁₈) are the main triglycerides detected in cornicle secretion. Trehalose is the most predominant sugar (558.2 mm), followed by glucose (92.0 mm) and inositol (48.8 mm). Many amino acids, including proline, glycine, alanine and serine, are also detected. In addition, the cornicle secretion is rich in many organic acids, including malic, citric, succinic and lactic acid. Information obtained from the present study improves our understanding of the chemical composition of the cornicle secretion of the brown citrus aphid.
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