Evidence of reproduction in the wild demonstrates initial success for reintroducing a critically endangered saproxylic hoverfly to a Scottish forest ecosystem

Saproxylic insects play a crucial role in forest ecosystems and serve
as indicators of forest health. Such species are sensitive to
commercial forestry management and have been historically overlooked by
conservation. Insects in general are underrepresented in conservation
translocation programs, but this is especially true for saproxylic
insects, among which saproxylic Diptera are particularly neglected,
despite being as speciose as better-studied orders like Coleoptera. Here,
we report on the first five years of a large-scale conservation breeding
and reintroduction effort for a saproxylic syrphid, the pine hoverfly
(Blera fallax), which, in the UK, was restricted to just one site in
Scotland and is classed as UK Critically Endangered. Starting
with 25 founders collected from the remnant UK population, our zoo-based
conservation breeding programme has produced ~8,000 pine hoverfly larvae
per year for three years. This, combined with extensive habitat management
at reintroduction sites, has enabled the release of 12,720 pine hoverfly
larvae and 43 adults across three sites over two
years. Post-release monitoring has so far found evidence of
successful pine hoverfly reproduction at two of our three reintroduction
sites. Despite these successes, we are conscious that we remain in the
establishment phase of the reintroduction programme. Our work
demonstrates that, with sufficient investment and resources, pine
hoverflies (and thus, potentially, similar species) can be bred at scale
for conservation release programmes, that releases of such species can
lead to successful reproduction in the wild, and that establishing
self-sustaining populations requires long-term commitment, which should
not be underestimated by those undertaking similar work.