SNH Species Action Framework: Pine Hoverfly

Management Actions and Achievements

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 Scottish Natural Heritage (SNH), the Malloch Society appointed a Project Officer to implement the first year’s actions in the agreed action plan to conserve the endangered pine hoverfly, Blera fallax.  Now three and a half years on, it’s time to report on the progress and achievements to date.

 

  

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Male Blera fallax, the pine hoverfly

 

 

Actions 1 and 2. Ensure the maintenance of viable populations and increase the amount of breeding habitat

Over 100 new breeding sites have been created within and around the remaining two B. fallax populations in Scotland.  Breeding sites were created by chain-sawing a triangular hole into the centre of a pine stump.  Sawdust is added to the hole and rainwater completes the job.  Ovipositing females are attracted to these holes and the larva filter feeds microbes from the liquid. 

 

Artificial B. fallax habitat creation: chainsaw-bored holes in pine stumps left after felling

 

Holes in stumps were made in 2003, 2006 and 2008.  Over the last three years, 36 holes have been occupied by over 400 larvae with a maximum of 30 individuals per hole.  Within the locality, larvae are now found over a wider area than before and the population seems to have increased.

 

B. fallax larvae removed from one rot-hole for counting and measuring, November 2009

 

Action 3. Increase the range from 2 to 5 localities by 2012

In 2008 preparations had begun to create habitat at the first relocation locality, a historic site for B. fallax, privately owned Rothiemurchus Estate.  By 2009 over 30 holes had been bored into spruce and pine stumps at three sites within 1km of each other. 

 

Habitat creation for B. fallax at the first relocation site: Rothiemurchus Estate

 

In October 2008, fifty larvae were removed from the field and reared in the lab to eclosion.  In May and June 2009, thirty eight surviving adults were moved to an on-site cage and four indoor cages in an attempt to captive breeding them.

 

On-site walk-in cage at Rothiemurchus Estate for captive breeding B. fallax

 

Adults required pollen, nectar, water, light and heat daily for between 5 and 14 days before they would begin to show signs of mate seeking behaviour. 

 

The adults preferred to feed on Rowan Sorbus aucuparia but also fed on a variety of flowering plants such as Greater Stitchwort Stellaria holostea, Heath Bedstraw Galium saxatile, Dog-rose Rosa canina, and a range of Umbellifers.

 

B. fallax feeding on a range of flowering plants

 

Once mated, females took one to two weeks to develop eggs before they would oviposit.  Inducing oviposition was only possible once females were sealed into large bags with water-soaked pine sawdust. 

 

Female B. fallax ovipositing eggs into water-soaked pine sawdust

 

 B. fallax eggs (within red circles, ~0.6mm long) on water-soaked pine sawdust

 

Three weeks after the first eggs had been oviposited tiny 1st instar B. fallax

 larvae could be seen.  In the first year, 5 females produced over 400 larvae.

 

First glimpse of 1st instar captive bred B. fallax larvae

 

In October 2009, 81 captive bred larvae were placed in holes, and in June and July 2010, 94 reared adults were released at Rothiemurchus Estate. 

 

Captive bred female B. fallax taking flight in Rothiemurchus Estate for the first time in 50 years

 

In August a new generation of larvae was found at Rothiemurchus Estate indicating a first-stage success at relocating B. fallax.  Forty-three new larvae were found in 12 bored-holes in pine stumps at Rothiemurchus Estate, four of which were 1km from the release site allowing a first estimate at the dispersal ability of this insect. 

In 2010 preparations had begun to create habitat at a second relocation locality, also a historic site for B. fallax, RSPB Abernethy Forest.  Here there were no stumps suitable for hole-boring so RSPB wardens felled one hundred pine trees of minimum 30cm diameter.  In an attempt to improve water-retention, holes were bored into the heartwood of the stumps using a drill avoiding the soft cambium.

 

 

 

 

 

 

 

 

Felled tree (top) and drilled hole in heart wood (bottom) to create breeding habitat for B. fallax at RSPB Abernethy Forest

 

In 2010, captive breeding was attempted a second time using the same methods.  Improving on the previous year, fifteen females produced over 700 larvae, 51 of which were moved into 12 bored holes at Abernethy Forest. 

Forestry Commission Inshriach Forest is currently being prepared as a third locality, where larvae are planned to be placed in October 2011. 

All three sites will be monitored, and the populations and breeding habitat annually supplemented.  It is proposed that captive breeding B. fallax will continue until relocated populations appear to be self-sustaining, a condition assessed through monitoring.

 

Action 4. Develop partnerships with interested parties and site owners and provide advice on habitat management for Blera fallax as required.

To mark the end of the SAF initiative for B. fallax a seminar will be held to present the work and discuss the future management of this species.  Attendees will include representatives from SNH, National Museums of Scotland, University of Stirling, Cairngorms National Park Authority, RSPB, Rothiemurchus Estate and other interested private landowners and managers. 

BBC AutumnWatch on the pine hoverfly