Ecology of a recently discovered exotic bee (Halictus smaragdulus) in Australia. Final report to the WV Scott Charitable Trust
The emerald furrow bee (Halictus smaragdulus Vachal, 1895), native to the Mediterranean was discovered (by chance) in the Hunter Valley, NSW, in late 2004. The possible undesirable effects of emerald furrow bees would include: competition with native species for floral and nest resources; transmission of parasites or pathogens to native organisms; changes in seed set of native plants (either increases or decreases); and pollination of weeds.
However, before determining the types of environmental impact that an exotic species has on an ecosystem, one must first determine which communities, and/or species are likely to be affected. Little was known about its ecology. This research therefore focussed primarily on determining the distribution of H. smaragdulus and native bee species, and relating patterns of distribution to environmental factors. In order to shed light on the history of this invasion, morphology of genitalia and DNA of the Australian population was examined to determine whether the incursion was likely the result of one or multiple events, and to identify a possible source population in Europe. Observations and sweep-netting over plants were also conducted to examine the plant species that H. smaragdulus may be pollinating, and therefore facilitating dispersal. Finally, 2 comparable methods of trapping were used to determine the best methods of surveying bees.
A number of different approaches were used to guide survey work. First, the climate from where the emerald furrow bee was found in Europe was used to identify areas across Australia that had a similar climate. A series of sites (100 in total) were chosen and sampling was conducted in October 2008. Second, 2 areas adjacent to where H. smaragdulus was already known were surveyed in November 2008 (94 sites) and December 2008 (97 sites). Third, the knowledge gained about the habitat preferences were used to target locations. A total of 78 sites were chosen using satellite imagery and the survey was conducted in March 2009. Fourth, specimens were collected above flowering plants using a sweep net. This method was done at random times and locations between the months of April 2008 and April 2009. Last, 35 community volunteers from the Hunter region were trained in the use of trapping methods via a specially produced video (made available on the YouTube website). Information packages were also sent to the participants, which included full-written instructions and trapping equipment.
Halictus smaragdulus was found across a much wider area of NSW than was previously known. The southern limits of its distribution were Sydney, and its Northern limit was Tamworth. Halictus smaragdulus was found as far west as Ulan, and Maitland in the east. Notably, the northern, western and eastern limits were the limits of our surveys, so it is possible that H. smaragdulus is present beyond these places. Surveys suggested that H. smaragdulus appeared to favour disturbed riverside habitats that supported weedy plant species and exposed sandy deposits. Sweep netting and direct observations over plants confirmed that H. smaragdulus is a generalist forager as it was found on a variety of plants including Gazania spp, Conyza canadensis, and Portulacca pilosa.
At least 14 species of bee (13 of which were native) are potentially threatened by H. smaragdulus. These 14 species were collected in the same traps as H. smaragdulus, and are assumed to be closely interacting. The abundance of bees at sites without H. smaragdulus was not different at sites with H. smaragdulus, therefore there was no evidence of population level effects. Inspection of genitalia indicated that there was only one form of the species present in Australia. However, this knowledge was of limited use in determining a source population because that form is present across its entire range in Europe. Unfortunately, European specimens were too degraded and DNA could not be extracted, however, DNA from specimens obtained from across the range in NSW signified 2 distinct maternal lineages, indicating that the incursion did not result from the introduction of a single individual.
The information gathered from this project suggests that H. smaragdulus has invaded a wide region of NSW. There was no evidence to indicate population-level effects on native bees, so it would be difficult at this stage to justify the cost of controlling/eradicating this species. Furthermore, it appears that H. smaragdulus is restricted, or at least present in much higher densities, in areas that are already highly disturbed and modified by humans. It is unlikely conservation managers will take action as there are no immediately apparent detrimental impacts.