Studies of elemental composition as a biological marker in insects. I. The influence of soil type and host-plant on elemental composition of Noctua pronuba (L). (Lepidoptera: Noctuidae)

Abstract

AbstractWavelength dispersive X-ray fluorescence spectrometry was used to make quantitative determinations of the elemental composition of adults of Noctua pronuba (L.) that had been reared on eight soil-plant combinations and a semi-synthetic diet. There were two host-plants, beans and lettuce, each grown in two clay soils of different acidity, a sand and a commercial potting compost. Analyses were done for fifteen elements: K, P, S, Mg, Ca, Cl, Zn, Si, Al, Fe, Cu, Mn, Ni, Cr and Ti. Two groups of elements were distinguished; the first six, or major elements, each with an average content about equal to or more than 1000 μg/g, and the last nine, or minor elements, each with an average content of <1000 μg/g. The second group was subdivided into four, Zn, Si, Al, Fe, each with an average content of >100 μg/g and four, Cu, Mn, Ni, Cr, of <100 μg/g; Ti was of erratic occurrence and was excluded from most statistical analyses. When all elements in all soil-plant combinations were considered, principal components analyses showed no distinction between insects reared on any soil-plant combination, probably because of interactions between host-plants and soils. When data were grouped into two host-plant subsets and only the major elements were analysed, soils were separable within each host-plant subset. In each case, the two clay soils were clearly separable from the other two soils but not from each other. In both host-plant subsets, sexes were distinguishable by a consistently higher K content in males. No clear separations were evident in either host-plant subset when all eight minor elements were considered or when these were separated into two further groups. This work indicates that (i) characteristic elemental compositions, or chemoprints, are present in N. pronuba; (ii) choice, not necessarily number, of elements is likely to be critical in describing and interpreting chemoprints; (iii) chemoprinting is unlikely to enable sources of populations to be identified in polyphagous species like N. pronuba; and (iv) the environmentally linked variation in chemical composition, affecting biologically essential elements, may have important consequences in the population dynamics of migratory and parthenogenetic species.