Monday, January 29, 2018

[Entomology • 2018] Megapropodiphora arnoldi • A Second Contender for “World’s Smallest Fly” (Diptera: Phoridae)

Megapropodiphora arnoldi
Brown, 2018

Flies of the family Phoridae (Insecta: Diptera) are amongst the most diverse insects in the world, with an incredible array of species, structures and life histories. Wiithin their structural diversity is the world's smallest fly, Euryplatea nanaknihali Brown, 2012.

New information:
A second minute, limuloid female phorid parasitoid fly (Diptera: Phoridae) is described. Known from a single specimen from a site near Manaus, Brazil, Megapropodiphora arnoldi gen. n., sp. n. is only 0.395 mm in body length, slightly smaller than the currently recognised smallest fly, Euryplatea nanaknihali from Thailand. The distinctive body shape of M. arnoldi, particularly the relatively enormous head, mesothorax and scutellum, the latter of which covers most of the abdomen, easily separates it from other described phorids. Most remarkably, the forelegs are extremely enlarged, whereas mid- and hind legs are reduced to small, possibly vestigial remnants. A possible male specimen, unfortunately destroyed during processing, is briefly described.

Keywords: tropical, parasitoid, biodiversity, taxonomy

Figure 2. Megapropodiphora arnoldi sp. n., female, dorsal view. Body length=0.395 mm.
Figure 3. Megapropodiphora arnoldi sp. n., female, ventral view. Legs re-arranged for easier viewing. Structure of mid- and hind legs approximate.
Drawing by T. Hayden.

Megapropodiphora  Brown, 2018, gen. n.
Type species: Megapropodiphora arnoldi Brown 2018, sp. n.

Diagnosis: There are a small number of minute, limuloid phorid genera in the world. In the New World tropics, the only relatively similar genera have large, differentiated frontal setae that are several times longer than the short frontal setae and do not have the scutellum covering the abdomen (Brown 1993). The Old World species of the genus Euryplatea Schmitz, likewise differ by having the abdomen not covered by the scutellum and by having a solid, triangular wing rudiment (Brown 2012).

Megapropodiphora arnoldi Brown 2018, sp. n.

Diagnosis: Female. Minute, limuloid; body setae scattered, sparse; wing with shed blades and short costa; head and scutum large, scutellum covering almost entire abdomen; oviscape thin, pointed, indicating a parasitoid lifestyle. Edge of scutum lateroventrally extended, posteriorly ending in narrowed flange (Fig. 4). Forelegs greatly enlarged; mid- and hind legs reduced.

Similar genera. Males of Brachycosta Prado, 1976, have a short costa, but much longer than that of Megapropodiphora gen. n., are much larger in size and have a larger frons and head. Females of this new genus are differentiated from all other phorids by minute size, leg structure and elongation of the scutellum to cover the abdomen.

Etymology: The genus name is Latin for large foreleg, referring to the structure of the female. The specific epithet refers to Arnold Schwarzenegger, former governor of California, whose own greatly enlarged forelimbs distinguished him in his pre-political careers.

Distribution: Amazonian Brazil

Biology: Unknown, but almost certainly a parasitoid. The torn wing membrane is reminiscent of other phorid flies that shed their wings when entering a social insect colony. It seems likely that the greatly enlarged forelegs are used to clutch a host, upon which the small, rounded body would appear similar to that of many phoretic mites.

Figure 4. Megapropodiphora arnoldi sp. n., female, dorsal, slightly oblique. Photomicrograph by B. Brown.

  Brian V. Brown. 2018. A Second Contender for “World’s Smallest Fly” (Diptera: Phoridae). Biodiversity Data Journal. 6; e22396.  DOI: 10.3897/BDJ.6.e22396

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