Orasema coloradensis Wheeler

Baker, Austin J. & Heraty, John M., 2020, The New World ant parasitoid genus Orasema (Hymenoptera: Eucharitidae), Zootaxa 4888 (1), pp. 1-84 : 14-18

Orasema coloradensis Wheeler

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( Figs 6 , 7 )

Orasema coloradensis Wheeler 1907: 12–14 .

Orasema coloradensis ; Gahan 1940: 441–442. Redescription and identification key.

Diagnosis. Orasema coloradensis is by far the most widespread and morphologically variable species in the coloradensis species group. It can be distinguished from O. scaura by the presence of five tarsomeres, a symmetrical labrum with four digits, and the flagellum being as long as or longer than the height of the head. It is distinguished from O. iridescens by a shorter female petiole (PTL:PTW = 1.0–2.0 versus 2.1–3.0 in O. iridescens ), shorter/wider antennae (female F2L:F2W = 1.4–2.0 versus 2.0– 2.5 in O. iridescens ), and having setose eyes ( Fig. 6B ).

This species is most similar to O. violacea , especially for some specimens collected in Florida and Texas, but is recognized by the finer, more costate sculpture on the mesoscutal midlobe compared to the coarsely areolate sculpture in O. violacea . Orasema violacea also tends to have a larger body size than many, but not all, specimens of O. coloradensis ( Fig. 7 ).

Description. Female. Length 2.4–3.7 mm ( Fig. 6A ). Color. Head and mesosoma a wide range of colors, but typically blue, green, or both. Scape, pedicel, anellus, and flagellum brown. Coxae iridescent blue-green; femora mostly dark brown with iridescent reflections, tips pale; tibiae pale brown. Gaster same color as mesosoma. Head ( Fig. 6B ). HW:HH = 1.1–1.3; face imbricate; eyes sparsely setose, IOD:EH = 1.5–1.7; MS:EH = 0.7–0.9; supraclypeal area as long as broad, equal to length of clypeus, smooth with shallow punctures. Labrum with 4 symmetrical digits. Occiput with dorsal margin rounded. Pedicel globose, as broad as F1. FL:HH = 1.0–1.4, F2L:F2W = 1.4–2.0, F2L:F3L = 1.2–1.8 ( Fig. 6D ). Mesosoma ( Fig. 6C, F ). ML:MH = 1.3–1.6. Mesoscutal midlobe transversely costate to areolate, densely setose; lateral lobe smooth to weakly imbricate. Axilla weakly sculptured, dorsally broadly rounded, with dorsal margin above dorsal margin of mesoscutellum; scutoscutellar sulcus narrow, regularly foveate, and broadly separated from transscutal articulation by deep foveae; mesoscutellar disc costate to areolate; frenal line regularly foveate; frenum weakly sculptured; axillular sulcus indicated by a weak longitudinal carina; axillula costate. Propodeal disc broadly rounded, without depression or carina, areolate-reticulate ( Fig. 6G ); callus weakly sculptured, costate anteriorly, densely setose. Propleuron weakly sculptured. Prepectus weakly sculptured. Mesepisternum weakly reticulate laterally, smooth ventrally. Upper mesepimeron weakly reticulate; lower mesepimeron smooth; transepimeral sulcus weakly impressed. Lateral metepisternum smooth medially but with foveae posteriorly. HCL:HCW = 1.4–1.9, weakly sculptured; HFL:HFW = 4.6–5.7. FWL:FWW = 2.3–2.5, FWL:ML 1.7–2.1; submarginal vein with several long setae; postmarginal vein slightly longer than stigmal vein. Metasoma. Petiole cylindrical, linear in profile, PTL:PTW = 1.0–2.0, PTL:HCL = 0.6–1.0, areolate, lateral margin with longitudinal carina continuous with basal flange, ventral sulcus absent. First (ventral) valvula with 6–8 small, narrowly separated teeth, second (dorsal) valvula with 8–10 annuli that are broadly separated dorsally, the carinae coalescing.

Male. Length 2.2–3.4 mm. HW:HH = 1.2–1.3. Scape dark brown; FL:HH = 1.3–1.6; anellus minute, difficult to distinguish; F2L:F2W = 1.3–2.3 ( Fig. 6E ). Femora mostly dark brown with iridescence, tips pale; tibiae pale brown. PTL:PTW = 2.2–3.4, PTL:HCL = 1.1–1.5.

Egg. Described by Johnson et al. (1986).

Planidium. The planidium of O. coloradensis was described by Johnson et al. (1986). They have been extensively observed on immature thrips, Sericothrips sp., indicating that this may be a commonly used intermediate host for this species ( Johnson et al. 1986), but it may be a facultative relationship because they mostly oviposit into leaves (occasionally stems and buds) ( Johnson et al. 1986) where immature thrips would not be expected to occur in high abundance. Other species oviposit exclusively into involucral bracts of unopened flower buds ( Johnson et al. 1986) where thrips density would be higher.

Hosts. Collected from nests of Pheidole bicarinata Mayr and Solenopsis molesta Emery in Colorado ( Wheeler 1907).

There is a record of O. coloradensis from the nest of Formica subnitens Creighton (Formicinae) ( Johnson et al. 1986). We consider this record to be erroneous because parasitized brood were never found; instead, the record was based on finding three Orasema adults in an emergence trap placed above a Formica mound, finding possible Orasema fragments within the nest, and finding one planidium attached to the maxilla of a Formica worker ( Johnson et al. 1986). Colonies of Solenopsis parasitized by O. coloradensis have been observed in cleptobiosis with colonies of Formica ( Wheeler 1907) , which may explain the observed association. It seems unlikely that Orasema could switch to another subfamily of ants with a pupal cocoon, which myrmicine ants lack. While other eucharitids can parasitize ants with pupal cocoons, and the maturing wasp pupa can be recovered from within the cocoon, this has never been observed within Oraseminae . Incidentally, an extensive two-year survey of Formica subnitens in Westbank , British Columbia, a locality where O. coloradensis has been collected, did not report finding O. coloradensis among the insects in or near the ant nests nor among the prey items of the ants ( Ayre 1957, 1958, 1959).

Plant associates. Gray rabbitbrush ( Asteraceae : Ericameria nauseosa (Pall ex. Pursh) G.L. Nesom & Baird), green rabbitbrush ( Asteraceae : Chrysothamnus viscidiflorus (Hook.) Nutt. ), and milkweed ( Apocynaceae : Asclepias sp.) in Idaho (specimen records; Johnson et al. 1986); western ragweed ( Asteraceae : Ambrosia psilostachya DC ), partridge pea ( Fabaceae : Chamaecrista fasciculata (Michx.) Greene ), and rushfoil ( Euphorbiaceae : Croton sp.) in Texas (specimen records); sidebeak pencilflower ( Fabaceae : Stylosanthes biflora (L.) Britton, Sterns & Poggenb.) and New Jersey tea ( Rhamnaceae : Ceanothus americanus L.) in Virginia (specimen records); and partridge pea, poorjoe ( Rubiaceae : Diodia teres Walter ), European turkey oak ( Fagaceae : Quercus cerris L.), and sandlace ( Polygonaceae : Polygonum dentroceras T.M. Schust. & Reveal ) in Florida (specimen records). Of these plant records, only Ericameria in Idaho and Chamaecrista in Florida have been independently confirmed as hosts, with O. coloradensis observed ovipositing into the leaves and stems of both of these plants.

Distribution ( Fig. 5 ). Canada: AB, BC, MB, ON; United States: AZ, CA, CO, FL, GA, ID, IL, IN, IA, KS, LA, MD, MO, MT, NE, NV, NJ, NM, NC, OK, OR, SC, TX, UT, VA, WA, WY; Mexico: NL, PU, SL, VZ. Collected June–August.

Material examined. Lectotype. UNITED STATES. Colorado: El Paso Co., Ute Pass , viii.1903 [♀ (female specimen with head intact, situated above one female and one male on the same card when lectotype viewed with head pointed left), by present designation for nomenclatorial stability, deposited in AMNH: UCRCENT00238021] . Paralectotypes. UNITED STATES. Colorado: El Paso Co., Broadmoor, near Colorado Springs , 11.viii.1903 [3♀, 1³, 15 pupae, AMNH: UCRCENT00238017–19]; Ute Pass, viii.1903 [1♀ (headless specimen), 1³, on same card as lectotype, AMNH: UCRCENT00238021] . Lectotype and paralectotype labels have been added to all relevant specimens. Larval slides. UNITED STATES. Idaho: Nez Perce Co., Hells Gate St. Pk., 293m, 46°21’24”N, 117°03’3”W ,

14.vii.1983, T.D. Miller, Ericameria nauseosa [1?, UCRC: UCRCENT00499476]. Texas: Kerr Co., Kerrville St. Pk., 500m, 30 ° 00’12”N, 99 ° 07’42”W , 24.vii.1988, Heraty, ovip. Grass [1?, UCRC: UCRCENT00499475]. Additional material examined. 736 specimens, see supplementary material.

There is some confusion regarding the type specimen of Orasema coloradensis . Wheeler (1907) was under the impression that O. coloradensis had already been described by Ashmead, which is made evident by his attributing the binomen to Ashmead as well as the identification. Johnson et al. (1986) attribute the binomen to Gahan, but as Gahan (1940) points out, Wheeler (1907) was in fact the first to publish this name. This confusion may be why the type material for this species is ambiguous. Wheeler (1907) did not directly designate type material, but he did provide a date (August, 1903) and locations (Manitou, Broadmoor, Beaver Ranch—all near Colorado Springs, Colorado) for material that he examined. The specimen currently designated as type (USNMENT00809501, type no. 27294) cannot actually be part of the type series because the specimen was from a series collected by C.F. Baker. There are four series of card-mounted specimens that we recognize as the syntypes collected by Wheeler in August, 1903 from Broadmoor (UCRCENT00238017–19) and Ute Pass, Colorado (UCRCENT00238021). Because the syntype series is from multiple hosts, we designate one of the female specimens as lectotype (UCRCENT00238021: there are three Orasema specimens on this card mount; the lectotype is the female with the intact head, which is placed above the other two specimens when viewed with the anterior end pointed left) and the remaining syntypes are designated as paralectotypes.

Discussion. There is a large amount of color and size variation in this species. In Texas, collection records show an enormous discrepancy in size ( Fig. 7D, E ), while in Florida, color varies to a large degree ( Fig. 7 H–J), and in Mexico, specimens have a slightly different head shape; however, despite this, all molecularly sampled specimens came out in a single highly-supported clade with little genetic variation ( Baker et al. 2020).

Figures

FIGURE 5. Distribution map of species in the Orasema coloradensis species group.

FIGURE 6. Orasema coloradensis. Female (UCRCENT00437137): A, habitus, lateral; B, head, anterior; C, mesosoma, lateral; D, antenna; F, mesosoma, dorsal. Female (UCRCENT00439136): G, propodeum, posterior. Male (UCRCENT00437137): E, antenna.

FIGURE 7. Comparison of the dorsal mesosoma of female Orasema coloradensis and O. violacea. All specimens scaled proportionately. A, O. coloradensis Lectotype from Colorado (UCRCENT00238021); B, O. violacea holotype from Florida (USN- MENT00809466);C,O.coloradensisfromColorado(UCRCENT00444500);D,O.coloradensisfromTexas(UCRCENT00320732); E, O. coloradensis from Texas (UCRCENT00397223); F, O. coloradensis from Idaho (UCRCENT00352500); G, O. coloradensis from Maryland (UCRCENT00414400); H, O. coloradensis from Florida (UCRCENT00411745); I, O. coloradensis from Florida (UCRCENT00139590); J, O. coloradensis from Florida (UCRCENT00404257).