AbstractEnergy-dispersive X-ray spectrometry was used to make quantitative determinations of the elemental composition of plasma-ashed apterous individuals of Rhopalosiphum padi (L.) and Metopolophium dirhodum (Walker). R. padi was reared on 24 plant–soil combinations and M. dirhodum on nine plant-soil combinations. Analyses were done for 12 elements: Na, Mg, Al, P, S, Cl, K, Ca, Mn, Fe, Cu and Zn. Principal components analyses of individuals showed no distinction, in either aphid species, between insects reared on any plant–soil combination, whether all elements, elemental sub-sets, soil sub-sets or host-plant sub-sets were considered. When group means (mean for all individuals from a particular plant-soil combination) were used in principal components analyses, five groups of R. padi could be distinguished from the other 19, although neither set could be further separated. Four of the five distinguishable groups were from plants that grew particularly poorly, and the fifth was from plants in a soil in which all host-plants grew less well than in other soils. There were no distinct separations between groups of M. dirhodum, though there were slight indications that soils were distinguishable. In both R. padi and M. dirhodum, elemental differences involved the minor elements, particularly Mn, Fe, Cu and Zn. The uniformity of elemental content in the apterae of both aphid species may be a consequence of genetic uniformity within clones of parthenogenetically reproducing species.
Occurrence of entomopathogenic fungi in populations of Metopolophium dirhodum (Walker) aphids feeding on primary and secondary host plants
