Restoring the endangered pine hoverfly in the UK

Summary

The pine hoverfly (Blera fallax), confirmed Endangered in the UK Red Data Book in 1999 after a 12-year study found it had declined from eight historic sites to just two in Scotland's central highlands, depends on rot-holes in decaying pine stumps where its larvae filter-feed, a microhabitat now rare in native pinewoods but occasionally found in plantations after felling. Building on artificial rot-hole techniques proven effective for a related species since the 1990s, University of Stirling researchers attempted the world's first captive breeding and relocation of any saproxylic insect, since direct wild-to-wild transfer was not viable. In November 2008, 50 larvae were collected from the wild; 38 emerged as adults in June 2009 across outdoor and indoor cages, mated, and laid roughly 460 eggs, producing about 300 surviving larvae. In October 2009, 85 captive-bred larvae were transferred into 28 bored stumps at a historic Scottish pinewood site, followed by release of 95 adults in June 2010, with remaining stock entering a second captive generation supplemented with fresh wild genetics to avoid inbreeding and captive adaptation. Monitoring found 60% of released larvae in stump holes after four weeks, dropping to 15% by eight weeks as larvae moved into leaf litter for winter; by August 2010, 43 new larvae were found in created holes, some a kilometer away. Major difficulties included near-total absence of prior ecological knowledge and a shortage of large pine stumps for durable rot-holes. The project rates itself Partially Successful, citing a new wild generation as an early positive sign despite its still-preliminary stage.