Abstract :
[en] The Giant balsam, Impatiens glandulifera Royle (Balsaminaceae) was introduced in Europe from the Himalayas as a garden ornamental plant in 1839. Due to its great success from nursery gardeners (1), it is now considered as one of the 100 worst invasive species in Europe. On the contrary, the native I. noli-tangere L. is considered to be in decline. Both species are annuals that absolutely need reproductive output to maintain or extend their populations. High fecundity has frequently been associated with invasiveness. However, traits controlling the reproductive success like pollinator attractiveness have not yet been assessed. The alien species is profusely visited by bumblebees which constituted the main visitors and efficient pollinators (2-3). The native also presents traits linked to insect attractiveness. Flowers produced similar quantities of nectar with the same sugar concentration and composition than the exotic. Therefore, the native could be considered as valuable source of nectar for pollinators. Despite the fact that nectar reward is likely to influence pollinator attractiveness, I. noli-tangere only occasionally received visits. Indeed, a flower of the native is 40 times less visited than a I. glandulifera flower (3). Differences in visitation rates may be explained by several factors, as floral scents, UV patterns or floral display.
In summer 2009, a first comparative study of floral scents between these two species was performed. An active sampling in a small glass chamber able to contain single flower left on the plant had been performed on a sorbent tube with Carbograph and Tenax TA. The volatiles of floral scents had been analysed by thermal desorption coupled to gas chromatography and mass spectrometry (4, 5). The composition of flower scents on the basis of area percent of identified peaks had been compared. Terpenes (d-limonene, α-terpinolene, p-cymene, α and β-terpineol) were emitted by the flowers of both species. Higher monoterpenes proportion in area percent was detected for the native species. Terpenes such as β-myrcene, 1,4-cineole, eucalyptol, carveol were absent in the flower scent of the alien I. glandulifera. However, the alien presented a higher alcane proportion. The implication of terpenes in the attractiveness of bumblebees will be studied.
