DOI: 10.5061/dryad.tht76hf9s
title: Evidence of reproduction in the wild demonstrates initial success for reintroducing a critically endangered saproxylic hoverfly to a Scottish forest ecosystem

description: 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.
description: # Evidence of reproduction in the wild demonstrates initial success for
 reintroducing a critically endangered saproxylic hoverfly to a Scottish
 forest ecosystem Dataset DOI:
 [10.5061/dryad.tht76hf9s](10.5061/dryad.tht76hf9s) ## Description of the
 data and file structure We collected data from our ex-situ breeding
 programme for pine hoverfly (*Blera fallax*) on dates of pupation, dates
 of adult emergence, sex, and adult lifespans in the adult flight season in
 2021, 2022, and 2023 at RZSS Highland Wildlife Park, Scotland. We also
 present data from pine hoverfly larval surveys at three release sites for
 animals from the breeding programme in the Strathspey area of the
 Cairngorms National Park. All missing data represented as NA. ### Files
 and variables #### File: AFD_2021.csv **Description:**  This file contains
 the raw data from 2021 to reproduce the analyses on the ex-situ breeding
 population at Highland Wildlife Park Variables in this file are coded as
 follows * Year laid: The calendar year that a given individual was
 prodcued as an egg - Pupa pot: Unique Identifier for that individual that
 year * Date pupa found: Calendar date the individual was found to have
 commenced pupation - note, this does not mean this was the exact date the
 individual commenced pupation as larval mesocosms are not checked for
 pupae daily - Sex: The sex of the individual - note sex can only be
 determined for adult flies so if the individual failed to emerge from
 pupation, the sex will be unknown * Death date: Calendar date each
 individual adult fly died - note, "Missing" in this field
 indicates that the body was never found and "Did not emerge"
 indicates that the individual failed to emerge from pupation -
 Euthanasia?: Indicates whether an individual lived its full lifespan or
 was euthanised by vets for welfare reasons - note, individuals that were
 euthanised were not included in calculations of mean adult lifespans *
 Adult lifespan (days): The lifespan of each individual in days NA values
 in the data indicate that no values are available for that variable. ####
 File: AFD_2022.csv **Description:**  This file contains the raw data from
 2022 to reproduce the analyses on the ex-situ breeding population at
 Highland Wildlife Park Variables in this file are coded as follows * Year
 laid: The calendar year that a given individual was produced as an egg -
 Pupa pot: Unique Identifier for that individual that year * Date pupa
 found: Calendar date the individual was found to have commenced pupation -
 note, this does not mean this was the exact date the individual commenced
 pupation as larval mesocosms are not checked for pupae daily - Sex: The
 sex of the individual - note sex can only be determined for adult flies so
 if the individual failed to emerge from pupation, the sex will be unknown
 * Death date: Calendar date each individual adult fly died - note,
 "Missing" in this field indicates that the body was never found
 and "Did not emerge" indicates that the individual failed to
 emerge from pupation - Euthanasia?: Indicates whether an individual lived
 its full lifespan or was euthanised by vets for welfare reasons - note,
 individuals that were euthanised were not included in calculations of mean
 adult lifespans * Adult lifespan (days): The lifespan of each individual
 in days NA values in the data indicate that no values are available for
 that variable. ### File: AFD_2023.csv **Description:**  This file contains
 the raw data from 2023 to reproduce the analyses on the ex-situ breeding
 population at Highland Wildlife Park Variables in this file are coded as
 follows * Year laid: The calendar year that a given individual was
 produced as an egg - Pupa pot: Unique Identifier for that individual that
 year * Date pupa found: Calendar date the individual was found to have
 commenced pupation - note, this does not mean this was the exact date the
 individual commenced pupation as larval mesocosms are not checked for
 pupae daily - Sex: The sex of the individual - note sex can only be
 determined for adult flies so if the individual failed to emerge from
 pupation, the sex will be unknown * Death date: Calendar date each
 individual adult fly died - note, "Missing" in this field
 indicates that the body was never found and "Did not emerge"
 indicates that the individual failed to emerge from pupation -
 Euthanasia?: Indicates whether an individual lived its full lifespan or
 was euthanised by vets for welfare reasons - note, individuals that were
 euthanised were not included in calculations of mean adult lifespans *
 Adult lifespan (days): The lifespan of each individual in days NA values
 in the data indicate that no values are available for that variable. ###
 File: WLS_2022.csv **Description:** This file contains the raw data from
 the 2022 pine hoverfly larval surveys in each of our three release sites
 in the Strathspey are of the Cairngorms National Park to reproduce the
 analyses on the released populations of pine hoverfly. All location data
 is redacted to protect this Critically Endangered Species Variables in
 this file are coded as follows * Site: Indicates which of the three
 release sites (identified as 1, 2, or 3) the data is from *** - Tree tag:
 Unique identifier for each artificial rot hole * Larval release date:
 Calendar date that pine hoverfly larvae were released into each artificial
 rot hole - Number of Blera fallax larvae released: The number of pine
 hoverfly larvae that were released in each artificial rot hole * Survey
 date: Calendar date of larval survey - Blera fallax: Number of pine
 hoverfly (Blera fallax) larvae detected in a given artificial rot hole
 during the larval survey * Myathropa florea: Number of Myathropa
 florealarvae detected in a given artificial rot hole during the larval
 survey - Calicera rufa: Number of Calicera rufa larvae detected in a given
 artificial rot hole during the larval survey * Xylota spp..: Number of
 Xylota spp.. larvae detected in a given artificial rot hole during the
 larval survey - Stump viability: Assessment made during larval survey of
 how much water each artificial rothole was holding NA values in the data
 indicate that no values are available for that variable. ### File:
 WLS_2023.csv **Description:**  This file contains the raw data from the
 2023 pine hoverfly larval surveys in each of our three release sites in
 the Strathspey are of the Cairngorms National Park to reproduce the
 analyses on the released populations of pine hoverfly. All location data
 is redacted to protect this Critically Endangered Species Variables in
 this file are coded as follows * Site: Indicates which of the three
 release sites (identified as 1, 2, or 3) the data is from** - Tree tag:
 Unique identifier for each artificial rot hole * Larval release date:
 Calendar date that pine hoverfly larvae were released into each artificial
 rot hole - Number of Blera fallax larvae released: The number of pine
 hoverfly larvae that were released in each artificial rot hole * Survey
 date: Calendar date of larval survey - Blera fallax: Number of pine
 hoverfly (Blera fallax) larvae detected in a given artificial rot hole
 during the larval survey * Myathropa florea: Number of Myathropa
 florealarvae detected in a given artificial rot hole during the larval
 survey - Calicera rufa: Number of Calicera rufa larvae detected in a given
 artificial rot hole during the larval survey * Xylota spp..: Number of
 Xylota spp.. larvae detected in a given artificial rot hole during the
 larval survey - Stump viability: Assessment made during larval survey of
 how much water each artificial rothole was holding NA values in the data
 indicate that no values are available for that variable.