Studies of elemental composition as a biological marker in insects. III Comparison of apterous and alate cereal aphids, especially Rhopalosiphum padi (L.) (Hemiptera: Aphididae), from oats and wheat, and from oats infected with or free from barley yellow dwarf virus

Energy dispersive X-ray spectrometry was used to make quantitative determinations of the elemental composition of plasma-ashed apterous and alate individuals of Metopolophium dirhodum (Walker) and Rhopalosiphum padi (L.). Both morphs of M. dirhodum were reared on wheat grown in potting compost as were the morphs of R. padi but the latter were reared also on oats, free from or infected with barley yellow dwarf virus (BYDV), grown in potting compost. The data were statistically analysed by various multivariate methods, which demonstrated that alatae of both species were more readily separated by their chemoprints than were apterae. There were also clear differences, again in both species, between the two morphs from wheat and the two from oats; the main discriminant elements for R. padi were Fe, Al and Mn, and for M. dirhodum they were Cl, Ca and Al. Alatae of R. padi from healthy and BYDV-infected oats were clearly differentiated from each other and from their apterae; both groups of apterae could also be separated but not as distinctly as the alatae. The discriminant elements for these separations were Fe, Zn and Mn, and possibly Al. The differences between alates, and between alates and apterae, may reflect fundamental differences in homeostatic and metabolic processes in alate and apterous morphs of R. padi.