ISSN 1911-2173

A product of the Biological Survey of Canada & the Entomological Society of Canada

Sciomyzidae of northeastern North America

Sarah Schorno1*

Stephen A. Marshall1

William L. Murphy2

Matthew J. Muzzatti1

1School of Environmental Sciences, University of Guelph, Guelph, Ontario N1G 2W1, Canada ([email protected], [email protected], [email protected])
27835 Tufton Street, Fishers, Indiana 46038 USA ([email protected])
*Corresponding author

Abstract

The 21 genera and 98 species of Sciomyzidae known from eastern Canada and the adjacent northeastern United States are keyed and illustrated. The eastern Canadian species are reviewed, with distributional maps and brief biological summaries provided for each species.

A corrigendum to this paper has been published (November 27, 2020) doi:10.3752/cjai.2020.AC06

 

Poecilographia decora (Loew) (photo by S.A. Marshall)

Introduction

The family Sciomyzidae (commonly known as snail-killing flies or marsh flies) is one of the best known dipteran families, in part because of the unique feeding behaviour of the larvae. Sciomyzidae is the only dipteran family with larvae almost exclusively obligate killers of molluscs (Murphy et al. 2012) and members of this family are the most frequently studied of all natural enemies of terrestrial gastropods (Barker et al., 2004). The feeding behaviour of larvae is diverse, ranging from saprophagous to predaceous to parasitoid, with many species having mixed or facultative behaviours (Knutson and Vala, 2011). Sciomyzidae have potential to serve as successful biological control agents of potentially harmful or destructive gastropods (Ehler and Miller, 1978).Adult Sciomyzidae are slender to robust flies, ranging in length from 1.7 mm (Colobaea americana) to 13.0 mm (Salticella stuckenbergi). They range in colour from shiny black (Pteromicra spp.), to dull gray or brown (many Pherbellia spp.), to subshiny brown (Tetanocera spp.) or yellowish (some Pherbellia spp.) (Knutson and Vala, 2011). Characteristically, adults fly quite low, slowly and for short distances, while their resting posture is often described as frog-like, with the head usually directed downward (Knutson and Vala, 2011). Sciomyzidae are readily distinguished from most other acalyptrate flies by a combination of external features including: antenna often porrect with elongated pedicel, oral vibrissae absent, postocellar setae parallel to slightly diverging, no more than two fronto-orbital setae, costa entire, subcosta complete, one or more tibiae with preapical setae, and clypeus inconspicuous (Barker et al., 2004; Knutson and Vala, 2011). Many other families of acalyptrate are sometimes confused with species of Sciomyzidae, especially Dryomyzidae, Heleomyzidae, and Lauxaniidae.The Holarctic region has the largest diversity of marsh flies, with 63 genera and more than half of the world’s fauna of 543 species (Murphy et al., 2018). Twenty-one genera and 98 species occur in eastern Canada and the adjacent U.S. states. All belong to the subfamily Sciomyzinae and can be readily segregated into two tribes, Sciomyzini and Tetanocerini, on the basis of presence or absence, respectively, of a well-developed proepisternal seta.Here, we provide a full-colour photographic key to the genera and species of Sciomyzidae of eastern Canada, including species not yet known from Canada but known from adjacent U.S. states, and possibly occurring but so far unrecorded north of the border between the U.S.A. and Canada.

Methods & Materials

Specimens
Specimens were obtained from the University of Guelph Insect Collection (DEBU, Guelph, Ontario, Canada), the Canadian National Collection of Insects, Arachnids and Nematodes (CNC, Ottawa, Ontario, Canada), the Royal Ontario Museum (ROM, Toronto, Ontario, Canada), and the National Museum of Natural History, Smithsonian Institution (Washington, DC, USA).

Geographic Limits of Study
Records for species in this study included those from the Canadian provinces east of Manitoba (Manitoba, Ontario, Quebec, Nova Scotia, New Brunswick, Prince Edward Island, Newfoundland and Labrador), and the adjacent northeastern states of the United States (North Dakota, South Dakota, Nebraska, Kansas, Oklahoma, Minnesota, Iowa, Missouri, Arkansas, Wisconsin, Illinois, Michigan, Indiana, Kentucky, Tennessee, Ohio, Maine, Vermont, New York, Massachusetts, Rhode Island, New Jersey, Pennsylvania, Maryland, Virginia).

Identification
Specimens were dissected when necessary for identification. Females of some genera (e.g. LimniaSepedon, and Tetanocera) are as yet unidentifiable to species and thus were determined to genus only. Male and female terminalia were examined after clearing whole abdomens in hot 10% potassium hydroxide (KOH) solution for approximately 8 minutes and subsequent neutralization in glacial (2%) acetic acid. Cleared structures were preserved in glycerin and pinned below specimens in microvials. Alternatively, abdomens can be cleared in hot lactic acid (abdomens cleared in lactic acid are less susceptible to ongoing deterioration than those cleared in KOH) or by use of enzymatic clearing (Yau and Marshall, 2015). The latter technique is safe, effective and utilizes clearing agents available in most pharmacies in the form of contact lens cleaning tablets, which is readily available even to the amateur naturalist.

Wing Interference Patterns (WIPs) Methods
WIPs were examined in 84 species across 21 genera of Sciomyzidae occurring in eastern Canada and the adjacent northeastern U.S. states. All of the specimens used were from the University of Guelph Insect Collection. WIPs were first observed on the dorsal surface of the wing under a stereomicroscope in front of a black background to ensure they were visible for photography. Entire WIPs were difficult to observe in preserved specimens that did not have their wings oriented properly prior to drying. A piece of black velvet was used as a background for photography. Wings were dissected from dry, pinned specimens and placed onto slides with one to two drops of 100% ethanol. A glass cover slip was placed on top to flatten the wing. Slides were prepared 24h before the photos were taken, giving the wings adequate time to dry before shooting. Slides were elevated above a piece of black velvet to reduce background artifacts. Pictures were taken using a Canon EOS 70D digital camera, an Infinity lens fit with a ring light, and a ML1000 Microptics Fiberoptic Illumination System, while using the software Helicon Remote (2016) to control the camera. Combinations of shutter speed and ISO, ranging from 1/8 sec to 4 sec shutter speeds and 125 – 250 ISO were used to take photographs. The photo-stacking program Helicon Focus (2015) was used to develop WIP photos. Images were processed using GNU Image Manipulation Program (GIMP) (2015) for Mac OSX. Image processing in GIMP was restricted to cropping, shading the background black, using the healing brush tool to neutralize dust from the wing surface, and adding up to 20% contrast. The wing terminology presented by Knutson and Vala (2011) was used to describe WIPs. For more information on WIPs, please consult Shevtsova et al. (2011).

Photography
Photograph stacks of whole specimens and diagnostic characters were taken with a Visionary Digital imaging system using a Canon EOS-1Ds camera. Stacks of images were combined by use of CombineZP software, and when appropriate, touch-up of images was conducted by use of Adobe Photoshop. Later images were stacked in Helicon focus and take using a Canon EOS70 and Helicon Remote to run a Stackshot motorized rail. Wherever possible, images of live flies were used to illustrate species habitus.

Maps
Distribution maps of species were created by use of Simplemappr open-access software (Shorthouse, 2010). The maps show specific localities (shown by dots) from various data sources (indicated by dot colour).

Locality Data
Distributional data were obtained from records of the University of Guelph Insect Collection (red dots on maps), the Canadian National Collection of Insects, Arachnids and Nematodes (yellow dot on maps), the late Benjamin A. Foote (green dots on maps), and from William L. Murphy (other institutions; purple dots on maps). Data from Benjamin A. Foote were included separately on maps to pay homage to his extensive personal collection of locality data for the Sciomyzidae family. William L. Murphy captured label data from specimens in the following collections:
CANADA: Ontario: Canadian National Collection of Insects, Arachnids and Nematodes (CNC), Ottawa; Great Lakes Forestry Centre (GLFC), Sault Ste. Marie; University of Guelph (DEBU), Guelph.
UNITED STATES: California: California Academy of Sciences (CAS), San Francisco; Essig Museum of Entomology (EMEC), University of California, Berkeley; Natural History Museum of Los Angeles County (NHM), Los Angeles. Connecticut: Peabody Museum of Natural History (PMNH), Yale University, New Haven. Delaware: University of Delaware (UDCC), Newark. Florida: Florida State Collection of Arthropods (FSCA), Gainesville. Illinois: Field Museum of Natural History (FMNH), Chicago; Illinois Natural History Survey (INHS), Champaign. Indiana: Purdue University (PURC), West Lafayette. Iowa: Iowa State University (ISUI), Ames. New Hampshire: University of New Hampshire (UNHC), Durham. New York: Cornell University Insect Collection (CUIC), Ithaca. Ohio: C.A. Triplehorn Insect Collection (OSUC), The Ohio State University, Columbus. Pennsylvania: Carnegie Museum of Natural History (CMNH), Pittsburgh; Pennsylvania Department of Agriculture (PADA), Harrisburg. Utah: Monte L. Bean Life Science Museum (BYU), Brigham Young University, Provo. Virginia: Virginia Polytechnic Institute and State University (VTEC), Blacksburg. Washington, DC: U.S. National Museum of Natural History (USNM), Smithsonian Institution.

Checklist

Anticheta (Key to species)

A. borealis Foote
A. canadensis (Curran)
A. fulva Steyskal
A. johnsoni (Cresson)
A. melanosoma Melander
A. robiginosa Melander

Atrichomelina

A. pubera (Loew)

Colobaea

C. americana Steyskal

Dictya (Key to species)

D. atlantica Steyskal
D. borealis Curran
D. expansa Steyskal
D. gaigei Steyskal
D. hudsonica Steyskal
D. laurentiana Steyskal
D. oxybeles Steyskal
D. pictipes (Loew)
D. steyskali Valley
D. umbroides Curran

Dictyacium (Key to species)

D. ambiguum (Loew)
D. firmum Steyskal

Ditaeniella

D. parallela (Walker)

Elgiva (Key to species)

E. connexa (Steyskal)
E. solicita (Harris)

Euthycera

E. flavescens (Loew)

Hedria

H. mixta Steyskal

Hoplodictya

H. setosa (Coquillett)

Limnia (Key to species)

L. boscii (Robineau-Desvoidy)
L. conica Steyskal
L. fitchi Steyskal
L. lindbergi Steyskal
L. loewi Steyskal
L. ottawensis Melander
L. sandovalensis Fisher and Orth
L. sparsa (Loew)

Oidematops

O. ferrugineus Cresson

Pherbecta

P. limenitis Steyskal

Pherbellia (Key to species)

P. albocostata (Fallén)
P. albovaria (Coquillett)
P. anubis Knutson
P. argyra Verbeke
P. beatricis Steyskal
P. griseicollis (Becker)
P. griseola (Fallén)
P. luctifera (Loew)
P. nana nana (Fallén)
P. obscura (Ringdahl)
P. paludum Orth
P. prefixa Steyskal
P. quadrata Steyskal
P. schoenherri maculata (Cresson)
P. seticoxa Steyskal
P. similis (Cresson)
P. suspecta Orth and Steyskal
P. tenuipes (Loew)
P. vitalis (Cresson)

Poecilographa

P. decora (Loew)

Pteromicra (Key to species)

P. albicalceata (Cresson)
P. anopla Steyskal
P. pectorosa (Hendel)
P. pleuralis (Cresson)
P. similis Steyskal
P. sphenura Steyskal
P. steyskali Foote

Renocera (Key to species)

R. cressoni Mathis and Knutson
R. johnsoni Cresson
R. longipes (Loew)
R. striata (Meigen)

Sciomyza (Key to species)

S. aristalis (Coquillett)
S. simplex Fallén
S. varia (Coquillett)

Sepedon (Key to species)

S. americana Steyskal
S. armipes Loew
S. borealis Steyskal
S. fuscipennis Loew
S. gracilicornis Orth
S. lignator Steyskal
S. neili Steyskal

Tetanocera (Key to species)

T. annae Steyskal
T. clara Loew
T. ferruginea Fallén
T. fuscinervis (Zetterstedt)
T. kerteszi Hendel
T. latifibula Frey
T. loewi Steyskal
T. melanostigma Steyskal
T. mesopora Steyskal
T. montana Day
T. oxia Steyskal
T. phyllophora Melander
T. plebeja Loew
T. plumosa Loew
T. robusta Loew
T. rotundicornis Loew
T. silvatica Meigen
T. spirifera Melander
T. valida Loew
T. vicina Macquart

Trypetoptera

T. canadensis (Macquart)

DNA Barcoding

Glossary

Glossary

General habitus

Male genitalia (Dictya and Limnia)

Male genitalia (Pherbellia and Sepedon)

Male genitalia (Tetanocera)

Wing Interference Patterns (WIPs)

Species Keys

Acknowledgments

The photos of Pteromicra albicalceata and the abdomen of Tetanocera kerteszii were provided by Brian V. Brown and Giar-Ann Kung (Entomology Section, Natural History Museum of Los Angeles County). The habitus shot of Renocera cressoni was provided by Torsten Dikow (Smithsonian Institution, USNM of Washington, D.C.) Other photos are by Stephen Marshall (live flies), William L. Murphy, Sarah Schorno, or Matthew J. Muzzatti. Wing interference pattern (WIP) images were taken by Matthew J. Muzzatti. The distributional maps included on the species pages were compiled in part by Hailey Ashbee (School of Environmental Sciences, University of Guelph).

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Cite

Schorno, S., Marshall, S.A., Murphy, W.L., and Muzzatti, M. 2019. Sciomyzidae of northeastern North America. Canadian Journal of Arthropod Identification 35: 331pp. doi:10.3752/cjai.2019.35