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

Taylor, Helen1; Allott, Carl1; Tompkins, Geneveive; MacGowan, Iain2

Published Jul 07, 2025 on Dryad. https://doi.org/10.5061/dryad.tht76hf9s

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Jul 07, 2025 version files 89.08 KB

Abstract

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.