SNH Species Action Framework: Pine Hoverfly
Management Actions and Achievements, July 2008
In July 2007, after formalising an agreement with the Royal Society for the Protection of Birds (RSPB), Forest Research (FR), National Museums of Scotland and SNH, the Malloch Society appointed a Project Officer to implement the first year’s actions in the agreed action plan to conserve the Pine Hoverfly, Blera fallax. Now one year on, it’s time to report on the progress and developments achieved by the action plan.
Male Blera fallax, the pine hoverfly (May 2008)
Action 1. Ensure the maintenance of viable populations.
As part of the Framework, current populations of B. fallax must be monitored and maintained. In October 2007, breeding sites were surveyed at one of the two B. fallax localities. These included both natural and artificial breeding sites (rot-holes and cut holes in pine stumps). The numbers of larvae in these holes were recorded. Survival to emergence of the adult is a key indictor of breeding success and by monitoring this we can test whether artificial breeding sites are working.
It is thought that much B. fallax mortality is due to harsh conditions experienced in winter. It was evident that B. fallax, and also the similar species Callicera rufa often avoid these conditions by moving out of their frozen liquid environment, awaiting thaw on the surface. This strategy may however increase their vulnerability to predators such as passerines.
C. rufa larvae exiting a frozen rot-hole (December 2008)
In April 2008, all artificial breeding habitats were surveyed to assess overwinter survival of larvae, and by May, 74 emergence traps were constructed over as many breeding sites to capture emerging adults.
Emergence traps erected over natural and artificial breeding sites (May 2008)
Few live B. fallax larvae were found in rot-holes, however in late-May, adults were found emerging from holes previously searched and assumed empty of larvae. In a controlled environment, B. fallax repeatedly moved out of the liquid throughout winter and pupated for 4-5 weeks before emerging in mid-May. It is thought that some larvae move out of the holes into surrounding vegetation early in the year thus adding to the complexity of environments upon which this species depends.
Two B. fallax (left) and 8 Myathropa florea larvae (right) found in an artificial breeding site (April 2008)
In order to assess abilities and preferences of B. fallax, survey and observation work is continuing. Understanding oviposition preferences of gravid females and factors effecting larval survival are critical components of managing B. fallax.
Actions 2 and 3. Increase the amount of breeding habitat at currently inhabited sites to increase the potential for further colonisation, and prepare breeding habitat at additional localities.
In order to determine the most favorable environment it is necessary to experiment with habitat creation techniques. The artificial and natural breeding habitat is being monitored and data collected to determine this. Such factors include changes in temperature, pH, and bacterial density.
Forty three artificial breeding sites have been created by boring holes in pine stumps and distributing plastic pots filled with pine chips where stumps were unavailable. Three more sites are intended for B. fallax habitat creation and expansion later this year.
Hole boring in previously felled pine stumps imitating the rot-hole breeding site (June 2008)
Action 4. Develop partnerships with interested parties and site owners and provide advice on habitat management for Blera fallax as required.
A Pine Hoverfly meeting took place on the 8th May 2008 hosted by Cairngorm National Park Authority (CNPA) to discuss current management and research, and prospects for future management and habitat expansion. Attendees included representatives from SNH, National Museums of Scotland, University of Stirling, Macaulay Institute, CNPA, RSPB and Rothiemurchus Estate.
Depending on the number of B. fallax individuals found this year and the relative health of the population, a new site is being developed with a view to translocate B. fallax towards the end of the year. Environmental factors within the holes and larval survival of similar species will be monitored to provide comparative data with currently inhabited sites.