Stegopterna diplomutata Currie & Hunter

Currie, Douglas C. & Hunter, Fiona F., 2003, A new species of Stegopterna Enderlein, and its relationship to the allotriploid species St. mutata (Malloch, 1914) (Diptera: Simuliidae), Zootaxa 214, pp. 1-11 : 2-6

Stegopterna diplomutata Currie & Hunter n.sp.

Cnephia mutata : of authors, not Malloch, 1914 (numerous references to diploid populations of the St. mutata complex)

Cnephia mutata '2n': Basrur 1957: 4 ­28

Cnephia mutata 'diploid form' Basrur & Rothfels 1959: 571 ­589

Stegopterna mutata : of authors, not Malloch, 1914 (numerous references to diploid populations of the St. mutata complex)

The name St. diplomutata is here associated with diploid (i.e., bisexual) populations of the St. mutata complex because triploid (i.e., parthenogenetic) populations are much more common of the two species in eastern North America. Accordingly, the name mutata probably applies validly to Malloch’s (1914) type for that species – a female from Glassboro, New Jersey.

MALE

Wing length ca. 2.5 mm. Scutum velvety brown. All hairs golden. Legs brown; calcipala large, lamellate, more than half as wide as apex of basitarsus. Terminalia ( Fig. 1 ): gonostylus not markedly tapered, bearing two medially directed spinules; ventral plate in ventral view moderately tapered anteriorly; paramere elongate, without apical spines (although closely associated with those adorning the aedeagal membrane); median sclerite with apex bifurcate.

FEMALE

Wing length ca. 3 mm. Scutum dark brown. All hairs golden. Mouthparts with mandibles serrated; lacinia with retrorse teeth; sensory vesicle about one­third as long as palpomere III. Legs brown; calcipala large, lamellate, more than half as wide as apex of basitarsus. Terminalia: anal lobe in lateral view with anterior margin scarcely sclerotized; genital fork with arms expanded into a large, subrectangular, lateral plate. Spermatheca almost spherical with polygonal pattern.

PUPA ( Fig. 2 ).

Length ca. 4 mm. Gill of 12 fine filaments arranged in two vertically divergent groups; a dorsal group of 7 filaments branching (1 + 2) (2 + 2), and a ventral group of 5 filaments branching (1 + 2) (1 + 1). Head and thorax with numerous rounded granules; trichomes simple. Cocoon a shapeless sac covering most of the body.

LARVA

Length ca. 6 – 7 mm. Body color grayish brown. Head capsule brownish yellow with contrastingly dark headspots. Antenna extended anteriorly well beyond apex of labral fan stalk. Hypostoma with teeth arranged in 3 prominent groups consisting of an elongate median tooth and two lateral lobes. Postgenal cleft inverted v­shaped, extending anteriorly as far as one­third the distance to hypostomal groove. Rectal papillae of 3 simple lobes.

TYPES

The type series was selected from a single locality because two or more species may be included under this name, which is here applied to all diploid populations of the St. mutata complex in eastern North America.

HOLOTYPE: Male, frozen dried, double mounted with minuten pinned through dorsum of scutum, and with pupal exuvia in glycerin pinned beneath in microvial. CANADA: Ontario, Nipissing District, Algonquin Provincial Park, Booth Lake, Booth's Rock Trail, 18 May 1992, F.F. Hunter.

The holotype and some larval paratypes are deposited in the Canadian National Collection of Insects, Ottawa. Additional paratypes are deposited in the Royal Ontario Museum, Toronto, the National Museum of Natural History, Smithsonian Institution, Washington, DC, and the Clemson University Arthropod Collection, Clemson, SC.

DERIVATION OF SPECIFIC NAME

The specific name is derived from the combination of “diplo” (a reference to the diploid configuration of the chromosomes) and “ mutata ”, the name of the closely related triploid species.

DIAGNOSIS

Stegopterna diplomutata is morphologically indistinguishable from St. mutata except for the presence of males in the former species. The male and female of St. diplomutata are easily distinguished from those of St. emergens and St. decafilis on the basis of their relatively large calcipala (half or more as wide as apex of basitarsus versus markedly less than half that width in the other two species). Furthermore, the lacinia and mandible of female St. diplomutata are armed with retrorse teeth and serrations, respectively. Such armature is lacking from the laciniae and mandibles of St. emergens and St. decafilis . Males and females of St. diplomutata are structurally similar to those of St. permutata and the other currently recognized cytotypes of Stegopterna from North America (viz., cytotypes 'O', 'W', and 'Y' of Madahar (1969)). However, St. diplomutata is distributed from the Great Plains eastward, whereas St. permutata and the informally named cytotypes occur west of the Great Plains.

Chromosomally, St. diplomutata and St. mutata differ from other members of the genus Stegopterna (e.g., St. emergens) by not having the fixed inversion IS­1 described by Madahar (1969). The IS­ 1 inversion has breakpoints (relative to the centromere) in the proximal region of section 3 and the distal region of section 6. Furthermore, St. mutata and St. diplomutata have the nucleolar organizer (NO) in the base of IL as compared with other species in genus Stegopterna which have the NO in the base of IS ( Madahar 1969).

Stegopterna diplomutata differs from St. mutata in the following features ( Figs. 3, 4 , and 5): St. diplomutata is diploid and St. mutata is triploid. The floating inversions IL­1, IL­2, IL­3, IL­4, IIL­1 and IIL­2 have been found in St. mutata (see Basrur and Rothfels, 1959), whereas floating inversions IS­1, IL­5, IL­6 and IIL­2 have been found in St. diplomutata . It is conceivable that additional floating inversions may be found in other as­yet undiscovered populations of both species.

BIOLOGY

The immature stages of St. diplomutata occur typically in small sized, low productivity, temporary­ or permanent streams. Aspects of population dynamics have been discussed previously by Davies (1950), Basrur and Rothfels (1959), Davies et al. (1962), Back and Harper (1979), and Adler and Kim (1986). In northern Ontario, St. diplomutata is among the earliest developing simuliids in the streams they inhabit ( Fig. 6 ). By the time larvae in the Simulium venustum /verecundum complex appear, St. diplomutata larvae have largely been replaced by those of the parthenogenetic St. mutata triploids.

Figures

FIGURE 1. Male terminalia of Stegopterna diplomutata n. sp.: a, ventral view; b, lateral view of ventral plate, median sclerite, paramere, and aedeagal membrane; c, terminal view of same structures; d, inner (dorsal) view of gonostylus; e, alternate view of ventral plate showing shape of posterior margin.

FIGURE 2. Pupa of Stegopterna diplomutata n. sp. in lateral view with cocoon removed.

FIGURE 6. Temporal succession of mature black fly larvae found at two different collection sites in Algonquin Provincial Park: Costello Creek, above and Booth’s Rock Trail Trickle, below. Along the x­axis, calendar week is given. Species are from four different genera: P., Prosimulium; Cn., Cnephia; St., Stegopterna; S., Simulium.

FIGURES 3 ­ 4. a, Chromosome photomicrographs of Stegopterna diplomutata; b, diagrams showing pairing of homologues. Fig. 3, IS, Short arm of Chromosome I showing a heterozygote for the IS­ 1 floating inversion; Fig. 4, IL, Long arm of Chromosome I showing a double heterozygote for the IL­ 5 and IL­ 6 floating inversions.