Micrurapteryx occulta (Braun, 1922) Braun, 1922

Kirichenko, Natalia, Triberti, Paolo, Mutanen, Marko, Magnoux, Emmanuelle, Landry, Jean-Francois & Lopez-Vaamonde, Carlos, 2016, Systematics and biology of some species of Micrurapteryx Spuler (Lepidoptera, Gracillariidae) from the Holarctic Region, with re-description of M. caraganella (Hering) from Siberia, ZooKeys 579, pp. 99-156 : 118-122

Taxon classification Animalia Lepidoptera Gracillariidae

Micrurapteryx occulta (Braun, 1922) comb. n. Figs 6-8, 9-10, 15, 21, 32-39, 44-46

Citations.

[ Parectopa occulta Braun, 1922: 91; McDunnough 1939: 98; Davis 1983: 9. Type locality: Powell County, Kentucky, U.S.A.]

[ Parectopa albicostella Braun, 1925: 213; McDunnough 1939: 98; Davis 1983: 9; syn. n. Type locality: Spring Hollow, Cache County, Utah, U.S.A.]

Type material examined.

Parectopa occulta : Holotype female, in ANSP, labelled: "B. 1071, | Powell Co., | Ky. i. VII. 12. 21 [handwritten]; "TYPE | Collection of | Annette F. Braun" [red, printed]; " Parectopa | occulta | Type Braun" [handwritten with top and bottom black border]; "Specimen ID | CNCLEP | 00123636" [printed]; "genitalia slide | JFL 1748 ♀" [pale green, printed except sex symbol handwritten]. The "B. 1971" refers to a Braun rearing lot number and corresponding sheet of rearing notes preserved with her collection in ANSP. In the original description ( Braun 1922) she provided the host information ( Vicia caroliniana Walter) and observations on the larval mine and cocoon.

Parectopa albicostella : Holotype male, in ANSP, labelled: "B. 1199" [handwritten]; "Cache Co. Utah | i. VIII.5.24 | Annette F. Braun" [printed, second line handwritten]; "TYPE | Collection of | Annette F. Braun" [red, printed]; " Parectopa | albicostella | Type Braun" [handwritten with top and bottom black border]; "♂ genitalia on | slide 3764 | D.R. Davis" [printed with black border, number handwritten]; "Photograph | on file | USNM" [printed with blue border]; "Specimen ID | CNCLEP | 00123635" [printed]. Regarding the type locality, the holotype labels indicated only "Cache Co." and no host but in her paper with the original description, Braun (1925) provided more precise information about the collecting site and indicated that it was reared from an undetermined “vetch” (presumably a herbaceous Fabaceae with Vicia -like foliage). The "B. 1199" refers to a Braun’s rearing lot number and corresponding sheet of rearing notes preserved with her collection in ANSP.

Other specimens examined.

See Tables 1, Suppl. material 1: Table S2.

Diagnosis.

Superficially, Micrurapteryx occulta is virtually indistinguishable from the other species treated here, especially when the substantial amount of individual variation in coloration is taken into account. Most specimens have the head, thorax, costal and dorsal margins and strigulae of the forewing white, contrasting sharply with the dark brown disk and ground color. However, in several specimens, the white areas are obscured by a suffusion of dark-tipped scales which gives them an overall dark, peppery appearance. The genitalia of both sexes are amply different from Micrurapteryx salicifoliella , the only other North American species (Figs 16, 22, 28, 29, 48). When compared to Palearctic Micrurapteryx , its genitalia are most similar to those of Micrurapteryx gradatella , from which it differs in having a single elongate cornutus and the latero-medial tooth projecting, whereas Micrurapteryx gradatella has a second cornutus consisting in a small, separate spine and its latero-medial tooth is elongate and flat. In the female genitalia of Micrurapteryx occulta , the posterior sclerotized papillate section of the ductus bursae is slightly shorter relative to the anterior membranous section, or less than half the length from the antrum to the corpus bursae; in Micrurapteryx gradatella , the papillate section extends to about two-thirds of the ductus length. The two species are closely related morphologically, genetically, and biologically.

Description of adult

(Figs 6-10). Wingspan 8.7-11.7 mm (average 10.1 mm; 44 specimens).

Head. Frons and vertex white in most specimens, or dark from admixture of dark brown scales in dark specimens. Labial palpus shape as in Micrurapteryx gradatella , outer surface of article 2 dark brown, inner surface from all white to nearly all dark brown; article 3 variously ringed with dark brown in distal half in many. Antenna dorsally fuscous throughout, ventrally with scale, pedicel, and in many ¼ to ⅓ of flagellum white; pecten absent.

Thorax. Dorsum white in pale (most) specimens, predominantly dark brown peppered with white in dark specimens. Tegulae dark brown. Legs as in Micrurapteryx gradatella .

Forewing. Pattern very similar to that of Micrurapteryx gradatella , but rather variable: in several specimens, dark portion of disk with pale-based, dark-tipped scales giving the appearance of pale suffusion; white dorsal margin in some specimens obscured by suffusion of dark-tipped scales; terminal portion between strigulae 4 and 5 and around apical spot rufous in specimens with white costa and margin. Forewing of darker specimens with overall peppery appearance.

Abdomen. (Figs 15, 21). Pale grey dorsally, white ventrally. In male coremata of intersegmental membrane 6-7 about 0.5 × width of S7.

Male genitalia (Figs 32-39, Suppl. material 2-4: Figs S01-S34). 32 preparations examined. Very similar to Micrurapteryx gradatella . Tegumen about 0.2 × length of valva, with long and thin peduncular arms, apex subtriangular or subconical, with jagged edge, sometimes slightly indented. A pair of elongate lamellae about as long as tegumen-peduncular arms bracing the sides of anal tube, their distal portion with oblique wrinkles. Anal tube with 1 or 2 setae in few specimens, without seta in most. Latero-medial spine of phallus simple in most specimens, bitoothed in some specimens (including the holotype of Parectopa albicostella ), tri-toothed observed in one specimen (Table 3), the spine projecting dorso-laterally from the phallus surface.

Female genitalia (Figs 44-46, Suppl. material 5-6: Figs S37-S52). 17 preparations examined. Very similar to Micrurapteryx gradatella . Sclerotized papillate section of ductus bursae about two-thirds length of ductus from antrum to corpus bursae. Number of spines of signa variable, 2-8 (average 5).

Notes about synonymy and variation.

The synonymy of Parectopa albicostella with Micrurapteryx occulta is here established based on examination of the type specimens of both nominal species. Braun described each species on the basis of a single specimen, which she reared. The holotype of Micrurapteryx occulta is a female reared from Vicia caroliniana , and that of Parectopa albicostella a male reared from an unspecified “vetch” ( Fabaceae ). We were not able to barcode the types. However, barcoded specimens of both sexes with genitalia corresponding to each of these nominal species cluster within a single, cohesive BIN (BOLD:AAD5802) comprised of specimens spanning a transcontinental geographic range. This cluster also includes specimens reared from different Fabaceae hosts that match the respective types in genital morphology and external appearance. Despite some morphological and genetic variation among examined specimens, we cannot find any consistent character to keep these two nominal taxa separate.

Braun (1925) indicated that Micrurapteryx albicostella was closely allied to Micrurapteryx salicifoliella Chambers (Fig. 11), Parectopa thermopsella Chambers, and Micrurapteryx occulta Braun, "but separated from all of them by the dark head and thorax and the white costal edge." We observed that these colour characteristics vary individually among all specimens examined, including among Micrurapteryx salicifoliella . For example, a pair of Micrurapteryx occulta with identical barcodes reared from leafmines on the same lupine plant from British Columbia (specimens CNCLEP00121158 and CNCLEP00121159) shows the male with a dark head and thorax as well as a darkened dorsal edge as exhibited by the male holotype of Parectopa albicostella , whereas the female has a white head, thorax, and costal edge as in the female holotype of Micrurapteryx occulta . In fact, the holotype of Parectopa albicostella has the thorax predominantly dark peppered with white scales (Fig. 8, not really “streaked” as Braun described). Although this might suggest sexual dimorphism in colouration, both colour patterns (and others) were observed in each sex among the other specimens that we examined.

The genitalia of both Braun holotypes are not distinguishable from those of other barcoded specimens in BIN BOLD:AAD5802, as well as from several additional non-barcoded specimens examined. Although minor variations in several features were observed, these do not exhibit a clear geographic pattern (Table 3).

In male genitalia (32 preparations examined, Figs 32-39, Suppl. material 2-4: Figs S01-S34), for example, the lateromedial tooth of the phallus is simple in most specimens (Fig. 33) but double in a few western specimens (Figs 35, 39, including the Micrurapteryx albicostella holotype from Utah), with one from British Columbia showing a suggestion of blunt doubling, and even one eastern specimen from New Brunswick with a triple tooth (Fig. 37); the apical lobe of the sacculus is variously pointed or somewhat rounded (rounded in Micrurapteryx albicostella holotype from Kentucky); the curvature of the apex of cucullus varies from well rounded to nearly straight; and a single or a pair of fine setae are present on the membranous part of the anal tube in some specimens (Fig. 32). The anal seta character is uncommon in Gracillariinae - it may have been overlooked - and seems inconstant at the specific level. One seta is present in one male Micrurapteryx kollariella examined (Fig. 30).

In female genitalia (17 preparations examined), the number of signa varies from 2 to 8 (average 5), and the relative length and thickness of the antrum, sclerotized portion of the ductus bursae, and ostium notch vary slightly in proportions with no significant gap (Figs 44-46, Suppl. material 5-6: Figs S37-S52).

On " Parectopa " thermopsella (Chambers, 1875).

Braun (1922, 1925) also alluded to the relatedness of Parectopa thermopsella to Micrurapteryx albicostella , Micrurapteryx occulta , and Micrurapteryx salicifoliella , highlighting slight differences in forewing streaks, and this suggests superficially a similar external appearance and forewing pattern. It is not known whether Braun had seen authentic Chambers specimens of Parectopa thermopsella . Chambers (1875) mentioned his Parectopa thermopsella as "closely allied" to Parectopa lespedezaefoliella (type species of Parectopa ), Parectopa robiniella , and Micrurapteryx salicifoliella , but his description of the larval mine immediately after that statement makes it unclear whether he was referring to the larval habits, the external appearance of the adult, or both. Both Parectopa lespedezaefoliella and Parectopa robiniella (Fig. 12) have forewing patterns unlike Micrurapteryx species but the larval mines are similar in appearance. The identity of Gracilaria [sic] thermopsella Chambers, 1875 remains unknown. The type locality is Spanish Bar, Colorado, and the host plant is a species of Thermopsis ( Fabaceae ). It has been included in Parectopa by subsequent authors ( Braun 1925, McDunnough 1939, Davis 1983) but no type or other Chambers specimens seem to exist (Don Davis, pers. comm. to JFL, 2015).

Note on transferring occulta from Parectopa to Micrurapteryx .

Despite the long-standing combination of occulta / albicostella with Parectopa , DNA, the forewing pattern, and genitalia clearly indicate greater relatedness to members of Micrurapteryx .

Biology.

Recorded host plants include several Fabaceae , namely Lathyrus japonicus Willd. [Syn. Lathyrus maritimus (L.) Fr.] (Quebec), Lathyrus sp. (California), Melilotus albus Medik. (British Columbia, Manitoba, Ontario, Connecticut), Vicia caroliniana Walter (Kentucky, type of occulta ), “vetch” (Utah, type of albicostella ), Lupinus sp. (British Columbia), Caragana sp. (British Columbia). It was collected in meadows, at the edge of forests, in open ponderosa pine forests (Washington), in alpine meadows (British Columbia), along the sea shore (Quebec), and probably other habitats, from sea level to high elevations in the mountains (Nevada), where suitable hosts occur. Records indicate two generations, at least over parts of its range, with most adult records in mid-summer. Early seasonal records in March - April as well as late-flying adults in October - December found indoors in southern Canada (Quebec, Ontario) suggest overwintering in the adult stage.

Distribution.

Micrurapteryx occulta is here recorded from across North America in the northern half of the continent, in Canada from the Maritime Provinces (Newfoundland, New Brunswick, Nova Scotia) to British Columbia, north to northernmost Yukon; in the United States it has been found in Connecticut (D.L. Wagner, pers. comm.), Kentucky, Illinois (T. Harrison, pers. comm.), Colorado (E. van Nieukerken, pers. comm.), Utah, Nevada, and California.