Canadian Journal of Arthropod Identification

An illustrated identification key to the genera of Ulidiidae (Diptera: Tephritoidea) of the United States and Canada

CJAI 44 -- April 26, 2021

Charles Wallace

| Abstract | Introduction | Materials & Methods | Checklist | Morphology | Generic Key | Acknowledgments | References | PDF | Cite |


The "picture-winged flies" (Ulidiidae) are one of the larger families of the Diptera superfamily Tephritoidea, numbering approximately 800 species total, about 135 of which are found in the United States or Canada (Steyskal 1987, Diaz-Fleischer et al. 2000) (some uncertainty remains regarding exact number, due to limited research, taxonomic revisions, and high number of Euxesta Loew). They are a family of acalyptrate flies, generally small to medium, and broadly recognizable by the distinctively patterned wings that grant the family its common name, though this trait is neither universal among nor exclusive to them. Traits common to the family are illustrated in Figure 1.

Figure 1. Lateral habitus of Xanthacrona bipustulata from the Smithsonian National Museum of Natural History collection, showing morphological traits common to Ulidiidae.

Currently, Ulidiidae is divided into two subfamilies: Ulidiinae and Otitinae, each with three tribes (and an additional incertae sedis group of genera in the latter) (Kameneva and Korneyev 2006). These subfamilies are unequally distributed geographically; Otitinae is primarily Holarctic, and represents the slight majority of species documented north of Mexico, whereas Ulidiinae is primarily concentrated in the Neotropical region of Central and South America (Arnett 2000, Kameneva and Korneyev 2006, Galinskaya et al. 2014).

Unlike its close relative, Tephritidae, the ulidiids are primarily a saprophagous group (Ferrar 1987; Arnett 2000). The greater number of picture winged flies can be found in association with feces or, more typically, rotting vegetables and fruits, where they commonly oviposit. Some publications (e.g. Arnett 2000) present the family as exclusively associated with plants, but, although there is a clear preference throughout the family for plant tissue, dead or alive, it is not exclusive (Ferrar 1987, Sivinski 2000, Marshall 2012). There is, however, a repeated trend within the Ulidiidae of true and/or opportunistic phytophagy, in which larvae act as primary, secondary, or tertiary invaders on living plant tissue (Kameneva and Korneyev 2010; Goyal et al. 2012). This is particularly well documented in those species that act as pests on plants such as sugar beet, onions, or corn (Ferrar 1987; Bjerke et al. 1992; Goyal et al. 2010, 2011, 2012).

Like the Tephritidae, adult ulidiids commonly use their distinctive wings to engage in often complex mating rituals. Male members of Callopistromyia Hendel raise their dappled wings at a 90 degree angle over their abdomen and "strut," while others such as Delphinia picta Fabricius make a "rowing" motion while walking over leaves (Sivinski 2000, Marshall 2012). Even more "extreme" examples of novel reproductive strategies can be found in species outside of a Nearctic distribution, as in the stalk-eyed Plagiocephalus Wiedemann, or the post-copulatory ejaculate expulsion in females of Euxesta bilimeki Hendel (Brunel and Rull 2010, Luis Rodriguez-Enriquez et al. 2013).

Unfortunately, the biology of many ulidiids, even in the relatively well-documented North American taxa, remains unknown or understudied. One potential barrier is the near absence of taxonomic tools. There is so far no comprehensive illustrated guide to the taxa of ulidiids of any biogeographical region, and many described species and genera remain to be photographed or otherwise imaged, or else are unavailable to a broad audience. This update to the key will fill some of this void by providing new images of many more taxa than have previously been available.