Biodiversity Data Journal :
Short Communication
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Corresponding author: Rob J. Deady (mycetophilid@gmail.com)
Academic editor: Vladimir Blagoderov
Received: 13 Sep 2022 | Accepted: 01 Dec 2022 | Published: 14 Dec 2022
© 2022 Rob Deady, Mark Delaney, Eleanor Jones, Peter Chandler
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Deady RJ, Delaney MA, Jones E, Chandler PJ (2022) Further interceptions of the Neotropical fungus gnat Sciophila fractinervis Edwards, 1940 (Diptera, Mycetophilidae) in Britain with comments and observations on its biology and spread. Biodiversity Data Journal 10: e94812. https://doi.org/10.3897/BDJ.10.e94812
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From 2020 onwards, several specimens of the Neotropical fungus gnat Sciophila fractinervis (Edwards, 1940) have been intercepted by Fera Science Ltd. on or near plant material in the United Kingdom originating from nurseries and glasshouses at four separate locations: Preston, Lancashire; Chichester, West Sussex; East Riding of Yorkshire; and Middlesbrough, North Yorkshire, as well as a single interception from the Netherlands. Gnat interceptions were associated with a wide range of plant species: Ficus benjamina, Ficus elastica, Dracaena reflexa var. angustifolia, Origanum vulgare, Rosmarinus officinalis, Thymus vulgaris, Impatiens hawkeri (Impatiens New Guinea hybrids), Chrysanthemum, as well as Fragaria vesca (var. Lusa). The species does not appear to be doing any damage to affected plants with growing conditions likely promoting multiplication under protection. The larvae likely feed on spores (generally saprophytic) adhering to webs they erect on the soil and around the base of plants with spores likely originating from the growing medium and plants. Their spread is likely facilitated by movement of the growing medium or plant material where pupae are suspended in the lower stem or leaf axils.
An account of the various interceptions is provided, as well as images of the different life-stages with a brief discussion of Sciophila cincticornis Edwards, 1940, its relationship with Sciophila fractinervis and further evidence of instability in vein R2+3 in the Sciophila genus.
Sciophila, Mycetophilidae, Fungus gnat, glasshouse, Neotropical
Fera Science Ltd. provides diagnostic support for the plant health service in England and Wales. The Plant Health and Seeds Inspectorate (PHSI) submit samples that they supect may be regulated or non-native to Fera for identification. Apart from gall midges (Cecidomyiidae) and darkwing fungus gnats (Sciaridae) (common pests in greenhouses), other members of the Sciaroidea, like the true fungus gnats (Mycetophilidae) and predatory fungus gnats (Keroplatidae) (such as Proceroplatus trinidadensis, Lane 1960, Fig.
Very few gnats are intercepted on produce into and out of the United Kingdom with few also detected on plants grown in nurseries. Above are examples of some of the species that have been confirmed. A Leia sp. intercepted on Zingiber from China. B Proceroplatus trinidadensis Lane, 1960 intercepted on Monstera deliciosa that originated from the Netherlands. C Sciophila corlutea intercepted on Prunus persica from Spain (likely adventitious).
Aside from these, one species that has been encountered more than others in recent times is the Neotropical fungus gnat Sciophila fractinervis (Edwards, 1940) (Fig.
The species was first recorded in Britain over 10 years ago by Peter Chandler from specimens recovered from a glasshouse in Warwickshire and apparently associated with Lisianthus (Eustoma grandiflorum) and potentially Christmas cacti (Epiphyllum) (
The immature lifestages of Sciophila fractinervis. A The larva of Sciophila fractinervis with close-up of cuticular ultrastructure made up of a mesh-like network on a decaying Chrysanthemum leaf. B The suspended pupa of Sciophila fractinervis surrounded by fine, filamentous webbing on Dracaena.
All gnat specimens were initially examined using a stereomicroscope (Leica 205C) with a Schott KL1500 LCD light source. All live larvae were examined by gently rolling them between the lid of a 150 mm × 15 mm Petri dish and the lid of a 60 mm × 15 mm Petri dish so as to view all characters required to identify the larva. Care was taken to avoid excessive pressure being applied to the specimens. Larvae were provisionally identified using a combination of
Symptomatic plants (with the larvae, pupae etc.) received were enclosed in sealed containers with breathing holes (sealed with mesh) and then placed in an incubator (240L Sanyo Co2 Incubator MIR-253) subsequent to visual examination where possible so as to rear these specimens to adulthood. In the case of the Middlesbrough finding, the pupa was placed on filter paper, in a Petri dish and sealed.
For adult gnat specimens submitted on sticky traps as in the case of the Preston finding, extraction and cleaning of the glue followed Appendix 1 (Protocol for removal of adult whitefly from sticky traps) in
Several strands of silk laid down by gnat larvae in the Dutch Chrysanthemum sample were examined for the presence of fungi. Strands were plated up on sterilised Petri dishes of PDA (Potato Dextrose Agar), incubated and identified on the basis of cultural, microscopic and morphological characteristics if possible.
Molecular methods
Two adult female gnats originating from East Riding of Yorkshire were sequenced for the COI DNA barcode (
Any fungi not identified using morphological means were identified via DNA sequencing in the Btub and ITS gene regions.
Larvae examined from Chichester, West Sussex exhibited all the characteristics of a Sciophila spp. larva. Under-developed antennae, well-developed maxillary palps, peripneustic in terms of spiracular layout and locomotory hooks being visible on the ventral surface of the body (presumably used to adhere to the webbing upon which it moved). It took 10 days for a single male fungus gnat to be reared from specimens on plants stored in the incubator and this was determined as Sciophila fractinervis (Edwards, 1940), a Neotropical species that is established in nurseries in the Netherlands (
Specimens from East Riding of Yorkshire (both female) were confirmed as Sciophila spp. and one close to S. fractinervis with the other close to S. cincticornis (Edwards, 1940). The suspected S. cincticornis generally followed the description by
Molecular results
COI DNA sequences were generated for the two reference samples, with two independent sequences generated per sample. Final sequence lengths were between 444 and 457 base pairs long. Both specimens had the same haplotype (i.e. they share the same DNA sequence), indicating they were likely the same species. There were no COI reference sequences for Sciophila cincticornis or Sciophila fractinervis on either the BOLD (
Not a great deal is known about the biology of the Sciophila genus nor the larval diet (
Growers, in many of the instances where S. fractinervis was found, noticed webbing forming on the compost surface (Figs
Other members of the Sciophilinae have been known to use webbing networks to effectively snare and feed on smaller invertebrates, but such feeding behaviour was not observed here or in the account by
To conclude, it appears that S. fractinervis is here to stay in Britain with interceptions and submissions to the lab on the rise as those in industry recognise symptoms of presence, larvae and the adults. More work ought to be carried out to ascertain the larval diet in an ex-situ context; however, saprophytic fungi likely sustain the larvae in a horticultural setting.
It is uncertain as to where the above-documented occurrences of the species originated. It is most likely the Netherlands, but in some instances, plants also originated from Costa Rica and Denmark. It is likely that this enigmatic species is more widespread than first realised especially in Europe. There is evidence that it is in the Republic of Ireland. Photos (Fig.
S. fractinervis does not appear to be doing any damage to the great many plant species it has been associated with under protection so far as we currently know. The webbing is viewed by the industry as "unsightly" and whether the webbing itself is facilitating any damage remains to be seen. In terms of control, Decis Protech (Bayer Crop Science UK) a deltamethrin-based insecticide has been shown to be effective at combatting older generations of S. fractinervis in glasshouses, but future generations appear to recolonise shortly after (pers. comm. Andrew Gaunt, PHSI/APHA). Alternatively, the Staphylinid biological control agent Atheta spp. which is effective against Ephydrids and Sciarids has been shown to be very effective (pers. comm. Neil Helyer, Fargro Ltd.).
This work was supported by the UK Government's Department of Environment, Food and Rural Affairs (Defra) under the Defra-Fera long term services agreement.
The authors would first like to thank Andrew Gaunt (PHSI/APHA), Neil Helyer (Fargro Ltd), Daryl Nightingale (PHSI/APHA) and Luke Lloyd for all the helpful information, photos and for submitting samples to the Fera entomology labs. Thank you to Aiga Ozilina (FERA) for isolating and identifying fungi and Dr. Chris Malumphy (FERA) for helpful edits and changes to the text. Thanks to all the FERA entomology team for the insightful discussions (Adele, Gemma, Sharon, Eleanor, Joe, Chris, Charlie, Rowan, Noel, James). Finally, thank you to several anonymous Bibionomorpha reviewers who provided invaluable suggestions and edits.
No potential conflict of interest was reported by the authors.