Orasema coloradensis

Baker, Austin J. & Heraty, John M., 2020, The New World ant parasitoid genus Orasema (Hymenoptera: Eucharitidae), Zootaxa 4888 (1), pp. 1-84 : 12-14

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Orasema coloradensis


Orasema coloradensis species group

( Figs 5–10 View FIGURE 5 View FIGURE 6 View FIGURE 7 View FIGURE 8 View FIGURE 9 View FIGURE 10 )

Established by Heraty (2000).

Diagnosis. Recognized by the following combination of characters: head and mesosoma with a moderate to dense amount of setation ( Figs 6B, C View FIGURE 6 , 9B, C View FIGURE 9 ), mesoscutal midlobe transversely costate ( Fig. 6F View FIGURE 6 ) to imbricate ( Fig. 9G View FIGURE 9 ) or areolate ( Fig. 10F View FIGURE 10 ), frenum in dorsal view elongate ( Fig. 9G View FIGURE 9 ), head subquadrate (length approximately equal to width) and with 4–6 labral digits ( Fig. 6B View FIGURE 6 ), mandibular formula 3:2, and antenna with 7 funiculars ( Figs 6D, E View FIGURE 6 ).

While this group is easily recognized among other Nearctic taxa, the most distinctive features (setation and sculpture) are homoplastic when compared to some Neotropical and Old World taxa.

Description. Female. Length 2.4–4.0 mm. Color. Mandible, maxilla, and labium brown. Wing venation pale brown. Head. Head in frontal view subquadrate; longitudinal groove between eye and torulus absent; malar depression weakly impressed adjacent to mouth; clypeus smooth with shallow punctures; epistomal sulcus distinct; anterior tentorial pit strongly impressed; anteclypeus distinct, nearly straight. Mandibular formula 3:2; palpal formula 3:2. Occiput imbricate, shallowly emarginate in dorsal view; temples absent. Scape not reaching median ocellus. Flagellum with 7 funiculars; anellus disc-shaped; funiculars subequal in length distally, equal in width; clava subovate. Mesosoma. Notauli deep. Mesoscutellar disc as long as broad. Propleuron convex. Mesepisternum broadly rounded anterior to mid coxa; postpectal carina weak. Hind femur evenly covered with short, dense setae. Fore wing basal area and speculum bare, costal cell and wing disc densely setose; marginal fringe relatively long; submarginal vein with several long setae; marginal vein with minute setae; stigmal vein slightly longer than broad, slightly angled toward wing apex. Hind wing costal cell with one or two irregular rows of setae. Metasoma. Antecostal sulcus foveate; acrosternite posteriorly rounded; apical setae of hypopygium present, minute.

Male. Length 2.2–3.4 mm. Without significant dimorphism except for slight differences in petiole length (male is longer and thinner than female) and a much smaller gaster.

Phylogenetics. All species within the coloradensis group except O. violacea have been molecularly sampled. Analyses using a few ribosomal and mitochondrial Sanger-sequenced loci, many Anchored Hybrid Enrichment (AHE) Illumina-sequenced loci, and a combination of both datasets resulted in a South American clade ( O. iridescens ) sister to a North American clade ( O. coloradensis + O. scaura ) ( Baker et al. 2020). Monophyly of each of the three sampled species has been confirmed, with O. coloradensis thoroughly sampled across its geographic range, including specimens from Colorado, Idaho, Texas, Maryland, Florida, and northeastern Mexico; the crown age for this species is estimated to be about 2–5 MY (varying between analyses) with an average of 5.3% sequence variation between AHE-sequenced specimens. The coloradensis species group is sister to the sixaolae species group + O. monstrosa ( Fig. 1 View FIGURE 1 ).

Discussion. Three trips were made to Idaho in 2013, 2015, and 2017 to collect O. coloradensis and O. scaura . Only a single specimen of O. coloradensis was collected among all three trips. Two additional trips were made to Hallelujah Junction, CA (near Reno, Nevada) to collect O. scaura , but no specimens were found. Two trips to Texas to collect O. coloradensis in 2014 and 2015 resulted in collecting several other species in the bakeri , cockerelli , and simulatrix groups but no O. coloradensis . Contrary to the other trips, collecting in Florida in 2014 resulted in an abundance of O. coloradensis specimens from multiple localities; however, no specimens that can be attributed to O. violacea have been collected since 1980. Low rates of collecting success in more arid locations has led us to consider the following hypotheses: 1) these species are highly ephemeral, possibly only emerging as adults for a few days at a time, making targeted collecting difficult; or 2) these species are locally extinct or in very low densities, possibly due to changes in ant fauna as a result of the spread of invasive ant species, including Solenopsis invicta Buren and Tetramorium caespitum (L.) (cf. Chien & Heraty 2018). While collecting in Hells Gate State Park, Idaho in 2013, James Johnson commented that the dominant ant in the area, T. caespitum , was not present when he was collecting in the 1980s, while the once-abundant proposed ant associate, Formica subnitens , was now extremely rare, and the host plant, gray rabbitbrush, was now largely absent from the area.

Key to species of the Orasema coloradensis species group

1) Legs with four tarsomeres ( Fig. 9E View FIGURE 9 ); labrum with 4–11 (usually 6 or 7), often irregularly shaped digits ( Fig. 9F View FIGURE 9 ); flagellum length shorter than height of the head (western Nearctic)..................................... Orasema scaura n. sp.

- Legs with five tarsomeres; labrum with 4 symmetrical digits; flagellum length as long as or longer than height of head..... 2

2) Eyes bare ( Fig. 8B View FIGURE 8 ); F2L:F2W = 2.0–2.5 (female), 2.1–2.3 (male); PTL:PTW = 2.1–3.0 (female), 3.4–4.2 (male) (Neotropical)............................................................................ Orasema iridescens n. sp.

- Eyes with sparse to moderate setation ( Figs 6B View FIGURE 6 , 10B View FIGURE 10 ); F2L:F2W = 1.3–2.0 (female), 1.3–2.2 (male); PTL:PTW = 0.9–2.0 (female), 2.2–3.3 (male).................................................................................. 3

3) Mesoscutal midlobe coarsely areolate ( Fig. 10F View FIGURE 10 ) ( United States: FL)........................ Orasema violacea Ashmead

- Mesoscutal midlobe transversely costate ( Fig. 6F View FIGURE 6 ) (widespread Nearctic)................. Orasema coloradensis Wheeler