Microdon mutabilis

{{Short description|Species of fly}} {{Speciesbox | image = Microdon mutabilis.jpg | genus = Microdon | species = mutabilis | authority = (Linnaeus, 1758) | synonyms = *''Microdon rhenanus'' Andries, 1912 *''Microdon scutellatus ''Schummel, 1842 *''Aphritis auropubescens ''Latreille, 1895 *''Mulio apiarius'' Fabricius, 1805 *''Microdon apiformis'' De Geer, 1776 *''Musca apiformis'' De Geer, 1776 *''Musca mutabilis'' Linnaeus, 1758 | synonyms_ref = <ref name=":3">{{Cite journal |last=Doczkal |first=Dieter |last2=Schmid |first2=Ulrich |date=1999 |title=Revision der mitteleuropäischen Arten der Gattung Microdon Meigen (Diptera, Syrphidae) |url=https://www.zobodat.at/pdf/Volucella_4_0045-0068.pdf |journal=Volucella |volume=4 |issue=1/2}}</ref> }}

'''''Microdon mutabilis''''' is a species of hoverfly. It is found in many parts of Britain and Europe, though it is quite rare and even listed as endangered in some countries.<ref name=":02">{{Cite journal |last=Schönrogge |first=Karsten |last2=Barr |first2=Boyd |last3=Wardlaw |first3=Judith C. |last4=Napper |first4=Emma |last5=Gardner |first5=Michael G. |last6=Breen |first6=John |last7=Elmes |first7=Graham W. |last8=Thomas |first8=Jeremy A. |date=2002 |title=When rare species become endangered: cryptic speciation in myrmecophilous hoverflies |url=https://academic.oup.com/biolinnean/article/75/3/291/2639623 |journal=Biological Journal of the Linnean Society |language=en |volume=75 |issue=3 |pages=291–300 |doi=10.1046/j.1095-8312.2002.00019.x}}</ref><ref name=":12">{{Cite journal |last=Scarparo |first=Giulia |last2=Cerretti |first2=Pierfilippo |last3=Mei |first3=Maurizio |last4=Di Giulio |first4=Andrea |date=2017-12-15 |title=Detailed morphological descriptions of the immature stages of the ant parasite Microdon mutabilis (Diptera: Syrphidae: Microdontinae) and a discussion of its functional morphology, behaviour and host specificity |url=http://www.eje.cz/doi/10.14411/eje.2017.071.html |journal=European Journal of Entomology |volume=114 |pages=565–586 |doi=10.14411/eje.2017.071|hdl=11573/1077239 |hdl-access=free }}</ref> The distinctive almost slug-like larvae live in ants' nests.<ref>{{cite book |last=Donisthorpe |first=H. St. J. |author-link= |date=1927 |title=The guests of British ants : their habits and life-histories |url=https://books.google.com/books?id=iBA5AAAAMAAJ&q=The+guests+of+British+ants. |location=London |publisher=Routledge |pages= 244 |isbn= }}</ref> They are hemispherical in shape, heavily armoured and believed to prey on the eggs and larvae of a number of ant species, including ''Formica lemani'', ''Formica fusca'', ''Lasius niger'' and ''Myrmica ruginodis''.<ref name=":5">{{cite book |author1=Stubbs, Alan E. |title=British Hoverflies: An Illustrated Identification Guide |author2=Falk, Steven J. |publisher=British Entomological & Natural History Society |year=1983 |pages=253, xvpp |name-list-style=amp}}</ref> It was described by Carl Linnaeus in his 1758 10th edition of ''Systema Naturae''.<ref>{{cite web |title=''Microdon mutabilis'' (Linnaeus, 1758) |url=https://www.gbif.org/species/124601343 |publisher=Global Biodiversity Information Facility |access-date=11 December 2018}}</ref><ref name=":4">{{cite book |url=https://www.biodiversitylibrary.org/page/727505 |title=Caroli Linnaei...Systema naturae per regna tria naturae :secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis |date=1758 |publisher=Impensis Direct. Laurentii Salvii |edition=10 |volume=1 |pages=592}}</ref>

== Description == {{Hatnote|For terms see Morphology of Diptera}}

=== Adults === thumb|Adult defining characters of ''Microdon mutabilis''. Pterostigma short: 2-2.5 times as long as the length of the costal section between distal ends of R1 and R2+3. Scutellum red or darkened.<ref name=":3" /> Photo by Abalg and Gunnar Engan (NBIC) ''Microdon mutabilis'' exhibits remarkable crypsis with its sister species, ''Mi. myrmicae'' in the adult stage. ''Mi. mutabilis'' adults are tentatively indicated to be distinguished from ''Mi. myrmicae'' by being 10{{Spaces}}mm or longer (adult ''Mi. myrmicae'' are said not to exceed 10{{Spaces}}mm).<ref name="Speight2">{{cite journal |last=Speight |first=M. C. D. |year=2011 |title=Species accounts of European Syrphidae (Diptera) |url=http://www.diptera.info/downloads/StN_Species_Accounts_Glasgow_2011.pdf |journal=Syrph the Net, the Database of European Syrphidae |volume=65 |pages=255, 285}}</ref> However, both species’ body length ranges between 9-11{{Spaces}}mm.<ref name=":0">{{Cite book |last=Van Veen |first=Mark P. |title=Hoverflies of Northwest Europe: Identification Keys to the Syrphidae |publisher=KNNV |year=2004 |isbn=978-90-5011-199-7 |edition=2nd |location=Utrecht |publication-date=2004}}</ref> Both ''Mi. myrmicae'' and ''Mi. mutabilis''are distinguishable from other ''Microdon'' species by the rust-red scutellum.<ref name=":11">{{Cite book |last=Ball |first=Stuart |title=Britain's hoverflies: a field guide |last2=Morris |first2=Roger |date=2015 |publisher=Princeton University Press |isbn=978-0-691-16441-0 |edition=2nd |series=WILDGuides |location=Princeton, New Jersey |pages=274}}</ref><ref name=":5" /> The scutellum has small scutellar spines.<ref name=":10">{{Cite journal |last=Coe |first=R. L. |date=1953 |title=Handbooks for the Identification of British Insects: Diptera. Syrphidae. |url=https://www.royensoc.co.uk/wp-content/uploads/2022/01/Vol10_Part01.pdf |journal=Royal Entomological Society of London |volume=10 |issue=1 |pages=89}}</ref><ref name=":3">{{Cite journal |last=Doczkal |first=Dieter |last2=Schmid |first2=Ulrich |date=1999 |title=Revision der mitteleuropäischen Arten der Gattung Microdon Meigen (Diptera, Syrphidae) |url=https://www.zobodat.at/pdf/Volucella_4_0045-0068.pdf |journal=Volucella |volume=4 |issue=1/2}}</ref> The dorsum of the head and thorax is clothed in light-golden hairs. The femurs are black, whereas the tibiae are covered in light beige hairs and the tibiae and tarsomeres are a rusty orange similar to the scutellum.<ref name=":12" /><ref name=":5" /> The wings are between 6–9{{Spaces}}mm in length.<ref name=":11" /> The antennae are elongate and the abdomen ranges from grey to black.<ref name=":4" /> The male genitalia are figured by Doczkal and Schmid (1999).<ref name=":3" />

=== Larvae === thumb|“Photographs of living Microdon mutabilis: A-second instar larva: A1-feeding on a larva of Formica cunicularia; A2-dorsolateral view; B-third instar larvae: B1-two larvae inside ant nest; B2-larva with a worker of Formica cunicularia; C1-adult emerging from puparium, anterior view; C2-adult with pupa”. From (Scarparo et al., 2017). <ref>{{Cite journal |last=Scarparo |first=Giulia |last2=Cerretti |first2=Pierfilippo |last3=Mei |first3=Maurizio |last4=Di Giulio |first4=Andrea |date=2017-12-15 |title=Detailed morphological descriptions of the immature stages of the ant parasite Microdon mutabilis (Diptera: Syrphidae: Microdontinae) and a discussion of its functional morphology, behaviour and host specificity |url=http://www.eje.cz/doi/10.14411/eje.2017.071.html |journal=European Journal of Entomology |volume=114 |pages=565–586 |doi=10.14411/eje.2017.071|hdl=11573/1077239 |hdl-access=free }}</ref> Figure authored by Andrea Di Giulio. Copyright CC-BY 4.0. The larval characters of ''Microdon'' are often more informative than adult characters due to morphological crypsis across the genus.<ref name=":12" /><ref name=":2">{{Cite journal |last=Scarparo |first=Giulia |last2=Wolton |first2=Robert |last3=Molfini |first3=Marco |last4=Pinna |first4=Luigi Cao |last5=Giulio |first5=Andrea Di |date=2020-06-09 |title=Comparative morphology of myrmecophilous immature stages of European Microdon species (Diptera: Syrphidae): updated identification key and new diagnostic characters |url=https://www.mapress.com/zt/article/view/zootaxa.4789.2.2 |journal=Zootaxa |language=en |volume=4789 |issue=2 |pages=348–370 |doi=10.11646/zootaxa.4789.2.2 |issn=1175-5334|url-access=subscription }}</ref> General descriptions of the larval characters are as follows:

The first instar is roughly ovular in shape and slightly tapered anteriorly. It averages to about 1.5 mm long and 0.8 mm wide. The pseudocephalon is visible at this stage. The body maintains a whitish color throughout all larval instars. The first instar is dorsoventrally flattened, though it does exhibit slight dorsal convexity. The sclerotized posterior spiracular tubule is elongate and light brown in coloration. Marginal band is fringed and traces around most of the body’s circumference except for anterior-most area.<ref name=":12" />

The second instar is considerably smaller and more circular than the first instar with an average length and width of 0.38 mm and 0.35 mm respectively. At this stage the dorsum is reticulated and roughly textured from various processes and microscupltures. The pseudocephalon is proportionately smaller and less visible. The posterior spiracular tubule is compressed into a dome and dark chestnut brown in coloration.<ref name=":12" />

The third instar averages at a length of 1.09 mm and width of 0.85 mm. This stage is more dome-shaped in comparison to the previous two instars. A light brown band of reticulation traces around the body’s circumference. Posterior spiracular tubule is reduced to a chestnut colored nub.<ref name=":12" />

The pupae are entirely sclerotized and retain the convexity of the third instar. They average to about 0.74 mm and 0.92 mm in width and length. The pupae are fully chestnut colored and have two anterior prothoracic spiracles as opposed to a single posterior spiracular tubule.<ref name=":12" />

Studies on pupal morphology indicate that ''Mi. mutabilis'' and ''Mi. myrmicae'' pupae can be distinguished by the following characters: ''Mi. mutabilis'' pupae are hairless, whilst ''Mi. myrmicae'' pupae are dorsally hairy. ''Mi. mutabilis'' is also indicated to have a more defined reticulation pattern than ''Mi. myrmicae.''<ref name=":2" /> It is also indicated that the anterior spiracles in ''Mi. mutabilis'' are equal in length and width or smaller, whereas they are longer and curved in ''Mi. myrmicae''.<ref name=":6">{{Cite journal |last=Van De Meutter |first=Frank |last2=Dekoninck |first2=Wouter |last3=Mortelmans |first3=Jonas |last4=Vantieghem |first4=Pieter |last5=Wakkie |first5=Bastiaan |title=First confirmed records of Microdon mutabilis and Microdon myrmicae (Diptera: Syrphidae) for Belgium |url=https://biblio.naturalsciences.be/associated_publications/societe-royale-belge-dentomologie-koninklijke-belgische-vereniging-voor-entomologie-1/srbe-145-2009/van-de-meuter-et-al-bulletin-145-vii-xii-116-120-2009.pdf |journal=Bulletin de la Sociétié royale belge d’Entomologie |volume=145 |issue=2 |pages=116-120}}</ref>

== Taxonomy == This species is part of the subfamily Microdontinae under the family Syrphidae, which is well known for its many instances of myrmecophily across the lineage.<ref name=":12" />

The generic epithet ''Microdon'' means “small tooth”, and refers to this genus’ scutellar spines.<ref>{{Cite book |last=Meigen |first=Johann Karl Wilhelm |url=https://www.biodiversitylibrary.org/item/137736 |title=Magazin für Insektenkunde |publisher=KarlReichard |year=1803 |volume=2 |location=Braunschweig |pages=275}}</ref> The specific epithet ''mutabilis'' refers to this species’ variable abdominal coloration ranging from gray to black according to the original description.<ref name=":4" />

The phylogenetic relationship between ''Microdon myrmicae'' and ''Microdon mutabilis'' remains a point of contention, with much of the discourse revolving around the species status lying in the host specificity and crypsis.<ref name=":12" /> ''Microdon myrmicae'' was formerly grouped within ''Microdon mutabilis'' until it was eventually separated in 2002 on the basis of ant host species and pupal morphology''.''<ref name=":02" /> However, records of potentially wider host ranges in ''Microdon mutabilis'' within the ''Formica'' genus including ''F. cunicularia'' and ''Lasius'' ''sp.'' challenges the validity of separating ''Microdon mutabilis'' and ''Microdon myrmicae'' solely on the basis of host species.<ref name=":12" /><ref name=":5" /><ref name="Speight2" />

Immature morphological characters do point towards possible phylogenetic relationships between species more reliably than adult characters in ''Microdon'', but it’s still difficult to reconstruct phylogenies solely based on these traits.<ref name=":2" />

== Habitat and distribution == The habitat range of ''Mi. mutabilis'' is highly dependent on its host species distributions.<ref name=":6" /> It is commonly found in grasslands, forest clearings and rocky areas where its host ant species reside.<ref name="Speight2" /> ''Mi. mutabilis'' is usually found with populations in drier, well-grazed areas in comparison to its sister species, Mi. myrmicae which prefers waterlogged, boggy areas.<ref name=":02" /> The larvae are often found in ''Sphagnum'' moss and under stones, where its hosts can also be located.<ref name=":5" />

''Microdon mutabilis'' is currently thought to be largely restricted in Great Britain and Ireland, though there have been recent rediscoveries of this species taking place in Belgium after it was thought to be extinct.<ref name="Speight2" /><ref>{{Cite journal |last=Van de Meutter |first=Frank |last2=Opdekamp |first2=Wout |last3=Mortelmans |first3=Jonas |last4=Versigghel |first4=Jan |last5=Mestdagh |first5=Cyr |date=2023 |title=Back in Belgium: Bracyhpalpus valgus (Panzwer, 1797), Mallota cimbiciformis (Fallén, 1817), Neoascia unifasciata (Strobl, 1898), Merodon moenium (Wiedemann, 1822) and Parhelophilus consimilis (Malm, 1863) (Diptera: Syrphidae) rediscovered. |url=https://www.researchgate.net/profile/Wout-Opdekamp-2/publication/380268896_Back_in_Belgium_Brachypalpus_valgus_Panzer_1797_Mallota_cimbiciformis_Fallen_1817_Neoascia_unifasciata_Strobl_1898_Merodon_moenium_Wiedemann_1822_and_Parhelophilus_consimilis_Malm_1863_Diptera_Syrphid/links/6633508406ea3d0b741fa516/Back-in-Belgium-Brachypalpus-valgus-Panzer-1797-Mallota-cimbiciformis-Fallen-1817-Neoascia-unifasciata-Strobl-1898-Merodon-moenium-Wiedemann-1822-and-Parhelophilus-consimilis-Malm-1863-Diptera.pdf |journal=Bulletin de la Société roale belge d’Entomologie / Bulletin van de Koninklijke Belgische Vereniging voor Entomomologie |volume=159 |pages=134-147}}</ref> The true host range of ''Mi. mutabilis'' remains widely unknown and requires reevaluation because past data was collected before ''Mi. mutabilis'' and ''Mi. myrmicae'' became separate species.<ref name="Speight2" /> This species is rare and females exhibit remarkably low dispersal rates.<ref name=":02" /><ref name=":7">{{Cite journal |last=Schönrogge |first=Karsten |last2=Napper |first2=Emma K. V. |last3=Birkett |first3=Michael A. |last4=Woodcock |first4=Christine M. |last5=Pickett |first5=John A. |last6=Wadhams |first6=Lester J. |last7=Thomas |first7=Jeremy A. |date=2008-02-01 |title=Host Recognition by the Specialist Hoverfly Microdon mutabilis, a Social Parasite of the Ant Formica lemani |url=https://doi.org/10.1007/s10886-007-9417-8 |journal=Journal of Chemical Ecology |language=en |volume=34 |issue=2 |pages=168–178 |doi=10.1007/s10886-007-9417-8 |issn=1573-1561|url-access=subscription }}</ref><ref name=":8">{{Cite journal |last=Elmes |first=G. W. |last2=Barr |first2=B. |last3=Thomas |first3=J. A. |last4=Clarke |first4=R. T. |date=1999 |title=Extreme Host Specificity by Microdon Mutabilis (Diptera: Syrphidae), a Social Parasite of Ants |url=https://www.jstor.org/stable/51167 |journal=Proceedings: Biological Sciences |volume=266 |issue=1418 |pages=447–453 |issn=0962-8452}}</ref> In instances where dispersion is recorded to have occurred in female ''Mi. mutabilis'', it took place over multiple decades. ''Microdon''’s poor ability to disperse renders this genus vulnerable to anthropogenic change in habitat.<ref name=":6" />

== Life cycle == ''Microdon mutabilis'' has an egg stage, three larval instars, a pupal stage, then adult stage.<ref name=":12" /> The female fly deposits batches of 3-6 eggs at host nests entrances (usually the nests of ''F. lemani'', but other hosts have been recorded). It is at this stage where they are most vulnerable to rejection by the host colony.<ref name=":8" /> The slug-like larvae then hatch after 10-14 days and prey on ant larvae and pupae.<ref name=":02" /><ref name=":8" /> The larval stage can last around 1-2 years, where the larvae undergo physiological and morphological changes as they complete their three instar stages.<ref name=":02" /> The larvae exhibit different growth rates and biennial larval duration as an adaptation to the myrmecophilous lifestyle, which is shared amongst other myrmecophilous insect groups.<ref>{{Cite journal |last=Schönrogge |first=K. |last2=Wardlaw |first2=J. C. |last3=Thomas |first3=J. A. |last4=Elmes |first4=G. W. |date=2000-04-22 |title=Polymorphic growth rates in myrmecophilous insects |url=https://pmc.ncbi.nlm.nih.gov/articles/PMC1690603/ |journal=Proceedings. Biological Sciences |volume=267 |issue=1445 |pages=771–777 |doi=10.1098/rspb.2000.1070 |issn=0962-8452 |pmc=1690603 |pmid=10819146}}</ref> The larvae pupate for another 14 days before the adult emerges. Adults only live for less than a week. These flies tend to sedentary, and males have been known to take advantage of this lifestyle by waiting at the entrance of nests to mate with females before they’ve even finished sclerotizing.<ref name=":02" />

== Host specificity == ''Microdon mutabilis'' locates its host species through volatile compounds such as methyl 6-methlysalicylate from ''F. lemani,'' which indicate host nest suitability for oviposition. Volatiles from ''M. scabrinodis'' were thought to be deterrents to females looking to oviposit. The compound methyl 6-methlysalicylate can be found in the mandibular glands of various Formicid lineages with different communicative functions, but these other lineages are allopatric to ''F.'' ''lemani'' which potentially explains the efficacy of using this compound as an orientation strategy. The function of methyl 6-methylsalicylate in ''F. lemani'' is postulated to be an alarm pheromone or serve as a chemical used for kin recognition. It seems unlikely that a single compound is used by these flies to orient themselves to potential host nests, though more studies are required.<ref name=":7" />

Female flies exhibit low dispersal and a high level of local specificity to certain nests within larger ''F. lemani'' populations. Past studies indicated higher egg survivorship in nests closer in physical proximity to the maternal nest, with higher egg rejection occurring as distance from the maternal nest increased. ''Mi. mutabilis’'' mimicry of host recognition compounds is indicated to be maternally inherited, and the relationship between survivorship and distance was thought to be related to the fact that ''F. lemani'' nests can be polygynous, where colonies are known to fragment but remain relatively genetically related to each other.<ref name=":8" /> More recent studies suggest higher genetic diversity within polygynous ant colonies for parasite defense leaves them more susceptible to social parasite infiltration due to more diversity in host recognition compounds.<ref>{{Cite journal |last=Gardner |first=M.g |last2=Schönrogge |first2=K |last3=Elmes |first3=G.w |last4=Thomas |first4=J.a |date=2006-10-11 |title=Increased genetic diversity as a defence against parasites is undermined by social parasites: Microdon mutabilis hoverflies infesting Formica lemani ant colonies |url=https://royalsocietypublishing.org/doi/full/10.1098/rspb.2006.3694 |journal=Proceedings of the Royal Society B: Biological Sciences |volume=274 |issue=1606 |pages=103–110 |doi=10.1098/rspb.2006.3694 |pmc=1679886 |pmid=17035169}}</ref> ''Mi. mutabilis’'' sister species ''Mi. myrmicae'' is less locally constrained because its host, ''M. scabrinodis'', exhibits more migratory behavior and tends to abandon its nests. ''F. lemani''—''Mi. mutabilis’'' host—exhibits higher fidelity to its nest location. Thus, ''Mi. mutabilis'' evolved stronger philopatry with its host nests whilst ''Mi. myrmicae'' resorted to bet hedging strategies to account for ''M. scabrinodis''’ nomadic nature.<ref name=":9">{{Cite journal |last=Scarparo |first=Giulia |last2=Rugman-Jones |first2=Paul |last3=Gebiola |first3=Marco |last4=Di Giulio |first4=Andrea |last5=Purcell |first5=Jessica |date=2021 |title=Social parasite distancing: RADseq reveals high inbreeding in the social parasite Microdon myrmicae but low philopatry for host ant nest |url=https://onlinelibrary.wiley.com/doi/abs/10.1111/een.12944 |journal=Ecological Entomology |language=en |volume=46 |issue=1 |pages=89–99 |doi=10.1111/een.12944 |issn=1365-2311|url-access=subscription }}</ref> Past records of more flexible host ranges in ''Mi. mutabilis'' challenged the extent of host specificity in this genus, and suggest that the notion of extreme host specificity may be locally constrained, however this continues to be an area where more research is needed.<ref name=":12" />

==References== {{Reflist}}

==External links== *{{cite web |url=http://www.boldsystems.org/index.php/Taxbrowser_Taxonpage?taxid=30761 |title=Taxonomy Browser: ''Microdon mutabilis'' |website=Barcode of Life Data System (BOLD) |access-date=July 12, 2020}} With images.

Category:Microdontinae Category:Flies of Europe Category:Insects described in 1758 Category:Animal taxa named by Carl Linnaeus