How Sweet is the Extra Floral Nectar Secreted by the Invasive Alien Tree of Heaven, Ailanthus Altissima Mill.? - Abstract
Tree of Heaven (ToH), Ailanthus altissima is a fast-growing tree native to China and Taiwan, but invasive in Europe and the U.S. where it disrupts urban and natural biocenoses. This invasive brings together successful strategies or traits including defense mechanisms and extrafloral nectaries. The Extra Floral Nectar (EFN) represents a significant energy source, owing to its carbohydrate-rich content, for visiting insects. The core ecological function of EFN is an indirect defense to plants by attracting insects (generally ants) that prey on herbivores or that deter herbivores from feeding on the plants. Assemblages of natural enemies associated to ToH were shown to include a large proportion of defoliators. Despite the importance of EFN, information on the sugar composition of EFN in ToH remains sparse. We analyzed by enzymatic assays the sugar composition of EFN in ToH plants from three locations in France. The total sugar concentration of EFN was not significantly different between locations unlike the hexose ratio. The ratio of sucrose to hexose, (r) ranged from 0.501 to 0.640, ranking ToH as a sucrose rich species. As it is generally admitted that sucrose rich nectars attract generalist ants and parasitoids, this finding represents a timely and a potentially fruitful avenue for future research addressing the ecological functions of EFN in ToH including indirect defences in relation to the assemblages of natural enemies associated with ToH in both native and invasive ranges.