A comparison of triglycerides from aphids and their cornicle secretions

Direct mass spectrometry of extracts showed that body triglycerides from 30 species of aphids contained the same fatty acid radicals, C₆ (hexanoyl), C_6:2 (sorboyl), C₁₄ (myristoyl), and C₁₆ (palmitoyl) as did the cornicle secretions, but in many species the proportions of hexanoyl and/or palmitoyl triglycerides were greater in the body. When cornicle secretions were collected progressively so as to draw increasingly upon body fat reserves, their composition changed gradually towards that of the body extracts.All summer forms of Myzus persicae had similar body triglycerides, even when selected for resistance to organophosphorus insecticides, or bred for 3 months on an artificial diet. The composition of body triglycerides was also independent of colour in two aphid species in which pink and green forms were compared.Body extracts contain enough triglycerides for their composition to be determined in single aphids and the use of body extracts allows examination of aphids lacking cornicles and of specimens that do not give cornicle secretion because of low body turgor. Although, as in the case of cornicle secretions, the triglyceride composition of body extracts was not well correlated with taxonomic position, body extracts provide a second chemical characteristic that can be used to define a particular species.