Exploitation of the invasive Acacia pycnantha pollen and nectar resources by the native bee Apis mellifera

Abstract

The importance of broad ecological perspectives has been well recognised with regard to the spread of alien species. However, less attention has been paid to single plant‐animal relationships such as the mechanism through which interactions with pollinators take place, which is responsible for the evolution of new mutualistic relationships and the outcome of sexual reproduction and distribution of plants. Because the majority of plant‐pollinator relationships are based on food collection by pollinators, we investigated the extent of exploitation of Acacia pycnantha by Apis mellifera. A. pycnantha is native to Australia, but is invasive in many Mediterranean countries, including Italy. We investigated whether visits by the native pollinator A. mellifera to a non‐native food source (A. pycnantha) were occasional, or dictated by a precise pattern matching resource availability. Showing that a native pollinator's foraging strategy has readily adapted to a potential resource offered by an invasive plant allows us to understand better the mechanisms promoting invasiveness of alien angiosperms. We collected data on pollen and nectar characteristics and variation in their availability, and conducted behavioural observations of foraging honey bees. Acacia pycnantha flower heads and extrafloral nectaries are sources of food actively selected by honey bees, which display behaviours strongly associated with resource availability. Our results showed clear evidence of a strong invasive plant‐native pollinator relationship, enhancing the success of sexual reproduction of the alien species. Future studies may highlight to which extent this relationship has influenced the spread of this invasive plant.

A botanic garden as a tool to combine public perception of nature and life-science investigations on native/exotic plants interactions with local pollinators

“…Bee visits on exotic flowers have long been recorded, even on invasive species from very distant origin [55]. Visitation rates may develop from occasional visits to the development of a given routine for resource collection [56]. From the results of the present study, we can conclude that the majority of visited plants in the GBG was actively looked for by local pollinators.…”

Why so many flowers? A preliminary assessment of mixed pollination strategy enhancing sexual reproduction of the invasive <i>Acacia longifolia</i> in Portugal

“…The honeybee can count on its behavioural plasticity to overcome handling inconveniences, including those associated with anemophilous species that lack a suitable landing surface (Giovanetti and Aronne, 2011). We then may expect the ubiquitous honeybee to be recorded on such inflorescences, as it was the case in the A. longifolia home range (Bernhardt, 1987), or on other acacias in invaded areas (Giovanetti et al, 2014(Giovanetti et al, , 2015Giuliani et al, 2016).…”

“…A. longifolia and A. pycnantha) are known to produce nectar, although on EFN (extrafloral nectaries), during the flowering season (Thorp and Sugden, 1990). Nectar produced by A. pycnantha was highly attractive to foraging honeybees in an invasion area in Italy (Giovanetti et al, 2015). Based on these features, it was long assumed that Acacia pollination is due to insects (Tybirk, 1997).…”

“…Bee activity perfectly matched the time of resource release, occurring at a different time of the day and, for nectar, also physically distant from the flowers. This happened notwithstanding the lack of a long-term co-evolution in time and space between the alien plant and the native pollinator (Giovanetti et al, 2015). The problem for sexual pollination of acacias in invaded areas is that the majority of species bloom at the very end of the winter, when weather conditions are still prohibitive for insect activity.…”

Functional Role of Extrafloral Nectar in Boreal Forest Ecosystems under Climate Change

“…In Italy, the invasive alien species Australian Acacia pycnantha Benth is an efficient foliar EFN producer in the afternoons, while pollen availability from flowers is highest in the mornings. Local honeybee populations have adapted to collect pollen from A. pycnantha flowers in the mornings and EFN from leaf phyllodes (modified petioles) in the afternoons [94]. A comprehensive assessment of the role of EFN in, e.g., honey production and the maintenance of pollination services in boreal and other forest ecosystems, remains to be carried out.…”