A Comparison of the Chemical Composition of Injured Leaves in Contrast to Uninjured Leaves of Victoria amazonica (Nymphaeaceae)

The object of this paper is to describe chemical and mineralogicalchanges in Victoria leaves that have sustained insect damage. Of 44 elements detected in various plant parts of Victoria amazonica(Poeppig) J. de C. Sowerby (V. regia auctt) Nymphaeaceae, only15 elements showed statistically significant differences inconcentration between insect-damaged leaves and whole (undamaged)leaves of the same plants. Two different types of insect damagewere noted: one was clearly recent, while the other was clearlyolder, probably not differing in time more than three weeks.Mg, Ca, Al, Si, S, Fe, Mn, Li and Ce were significantly moreconcentrated in the damaged leaf sections than in undamagedleaves of the mature plants with unopened buds. In the caseof preflowering plants, Na, Mg, Ca, Al, Si, S, Cl, Fe and Mnwere more prevalent in the damaged tissue than in the unattackedleaves of the same plants. In the former case, Na, K, Cl andP are rapidly lost when damage occurs, while plants that havehad a chance to recover from the damage, as in the case of thepreflowering plant leaves, begin to make up the difference inelemental concentration between the damaged and undamaged leaves. Mineralogical investigation showed that the amount of calcite(CaCO₃), the calcium oxalates weddellite and whewellite, andthe siliceous minerals - low-form cristobalite opal, low-formtridymite opal and quartz-was higher in the recently injuredleaves than in those that had been injured some time previouslyor than in the uninjured leaves. It is hypothesized that theincreased precipitation of minerals resulting from injury ispart of the plants' defence mechanism against further attackby insects or animals. Insect injury, Victoria, leaves, inorganic composition, mineralogy     

The chemical composition of Astragalus: a comparison of seleniferous and non-seleniferous plants growing side by side

COWGILL, U. M. & LANDENBERGER, B.D., 1992. The chemical composition of Astragalus: a comparison of seleniferous and non-seleniferous plants growing side by side. This paper describes how non-seleniferous plant species coexist with seleniferous ones and what chemical changes occur in non-seleniferous species that allow the toleration of large quantities of volatilized Se-bearing compounds. These compounds are known for their phytotoxicity as well as for their toxicity to mammals and insects. Twenty-three sites (Colorado, Utah, New Mexico, U.S.A.) were examined over a 6-year period. Plants collected from these sites were divided into four groups: seleniferous astragali, seleniferous Brassicaceae, non-seleniferous astragali and non-seleniferous associated genera. Furthermore, it was possible to categorize these sites: Type 1 sites supported all four groups of plants, Type 2 sites contained only seleniferous astragali, whereas Type 3 sites sustained only non-seleniferous astragali. When concentrations of Cu, Zn (P <0.0001), Si (P<0.02), As, Pb (P<0.03) and Cs (P<0.05) were measured, the values for those seleniferous astragali that coexisted with other species were significantly different from the values found for those seleniferous astragali that grew alone. There were four areas that in some years supported all four groups of plants (Type 1 site) and in other years contained only seleniferous astragali. In this way, the latter may be used as a chemical control for the former. The seleniferous astragali collected at Type 1 sites always contained more Cu, As, Si and Pb than the solitary astragali of Type 2 sites. When seleniferous astragali of Type 1 sites that support all four groups of plants develop in a year where the usually associated species of past years are absent, they contain in their tissues concentrations of Cu, As, Si, Pb, Zn and Cs typical of Type 2 sites where the seleniferous astragali grew alone. Non-seleniferous astragali of Type 1 sites that support all four groups of plants have a chemical composition that differs significantly in the quantity of 15 elements from non-seleniferous astragali of Type 3 sites where the latter grew alone. Since allelochemicals such as phenolic acids and flavonoids are well known to be able to alter mineral absorption by plants and since the astragali are known to produce such substances, it is suggested that the possible production of phenolic acids and flavonoids may permit coexistence of seleniferous plants with non-seleniferous ones and thus explain the chemical differences among the plants of the four types of sites.     

The selective use of floral resources by the hoverfly Episyrphus balteatus (Diptera: Syrphidae) on farmland

The use of flowers of non-crop plants by the syrphid Episyrphus balteatus in margins of cereal fields was assessed quantitatively. G-tests and the ‘C’ index of Murdoch (1969) were used to compare the use and abundance of twenty-seven plant species by adult flies from June to August in the UK. The flowers of several plant species were used selectively by hoverflies throughout the season while the relative importance of others changed with date. The prospects for managing the field-margin flora to enhance biocontrol by hoverflies is discussed.