The major carotenoid pigments of the grain aphid, Sitobion avenae (F.) (Hemiptera : Aphididae)

The economically important grain aphid, Sitobion avenae (F.) shows colour p olymorphism with brown and green forms predominating. Colour is determined both genetically and in response to environmental factors, including nutrit ion. The biological significance of the colour polymorphism is unknown, alt hough seasonal changes occur in the frequency of colour morphs in the field , whilst the brown morph may have adaptive significance in terms of hymenop terous endoparasitism. The ground colour of aphids is produced by haemolymp h pigments, aphins (glucosides) and carotenoids. The latter may be under th e synthetic control of intracellular endosymbiotic bacteria. In this study, the major carotenoid pigments of a brown and a green clone of S. avenae we re examined using thin layer chromatography (TLC) and high-performance liqu id chromatography (HPLC), and their absorbance spectra recorded. Using TLC, the brown clone produced five bands of different Rf, ranging from yellow, to orange-pink to pink in colour. In contrast, the green clone gave only a single yellow band of higher Rf than any of the bands of brown aphids. Foll owing separation of carotenoids by HPLC, brown aphids gave seven peaks and green aphids five. Comparison of absorbance maxima with known published val ues for carotenoids provides strong evidence for the identification of four of the carotenoid pigments from brown aphids (RB-4, 3,4-didehydrolycopene; RB-5, torulene; RB-6; lycopene; RB-7, gamma-carotene) and one from green a phids (RG-2, a-carotene). The other carotenoids remain unidentified. The bi osynthesis and possible biological relevance of the various pigments of S. avenae are briefly discussed.