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The aim of this study was to investigate the pollen morphology and the ranges of intraspecific and interindividual variability of the North American steeplebush— Spiraea tomentosa L., an invasive species in Poland. Steeplebush inflorescences were collected randomly from 30 localities of S . tomentosa in Poland. In total, 900 pollen grains were analysed with both a light and a scanning electron microscope. Nine quantitative and three qualitative pollen features were studied. The diagnostic features were: exine ornamentation (size and direction of the muri), operculum and perforation size. For the first time, the intraspecific and interindividual variability of the pollen grains of the highly invasive S . tomentosa were investigated. Pollen grain features were so similar, that they did not allow to differentiate individual samples of S . tomentosa and only groups of samples were recognized.

The introduction of alien species can have a significant impact on the food preferences of native phytophagous insects. The moth Earias clorana L. has previously been considered to be monophagous, ingesting only plants in the genus Salix. In recent years, we have observed larval E. clorana feeding on Spiraea tomentosa L., an invasive shrub species in Central Europe that is native to North America. We hypothesised that this insect can feed on Spiraea tomentosa leaves with no negative effects on its growth and development, and that the leaves of Spiraea tomentosa as a source of food for E. clorana are equally as good as leaves of Salix viminalis L. Our results showed that despite significant differences in the chemical composition of the studied species' leaves, including a much higher concentration of defence compounds (total soluble phenols and condensed tannins) in Spiraea tomentosa leaves than in those of Salix viminalis, feeding on a new host plant did not significantly affect the survival of larvae. The change in host plant had an unfavourable effect, however, on several parameters of growth and development for the larvae (masses of larvae and pupae, relative growth rates, and efficiency of conversion of ingested food). We conclude that, in comparison to Salix viminalis, Spiraea tomentosa is not a particularly favourable food for larval development. Perhaps, even without direct improvements in adult foraging efficiency, however, the costs of switching hosts may be minimised in larvae that develop on very abundant, invasive species, such as Spiraea tomentosa in Central Europe.

Due to the threat posed by the spread of invasive plant species, there is an urgent need to develop effective methods of eradicating and managing their biomass. The aim of the study was to examine selected invasive plants in terms of their use for energy purposes and to find out whether they can be a raw material for the production of second-generation biofuels. First, their chemical compositions were determined. The higher heating value (HHV) and lower heating value (LHV) were also calculated. High values of the higher heating value, ranging from 18.490 MJ∙kg−1 to 19.900 MJ∙kg−1, indicate the possibility of using the biomass of invasive plants for energy purposes (combustion). All investigated invasive plant species were also subjected to the process of obtaining ethanol. This included an alkaline pretreatment with 1% sodium hydroxide, followed by a simultaneous saccharification and fermentation (SSF) process. The highest ethanol yield per ha of plants was obtained at 2.6 m3∙ha−1 for the Reynoutria × bohemica biomass. The remaining species showed an ethanol yield below 2 m3∙ha−1. The conducted research allows for the conclusion that the studied invasive plants can be a promising raw material for the production of bioethanol.