Tetracnemus

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1 Brachypterous………………………………………………………………….…… sp. 4
1’ Fully winged …………………….….……………………………………………..….. 2

2(1) Funicle segments 1-3 or 1-4 lightened ………………………………………….. sp. 2
2’ Funicle completely dark …………….………………………………………………… 3

3(2) Ovipositor sheaths about equal in length to metasoma…..………..…………… sp. 1
3’ Ovipositor sheaths about 50-60% length of metasoma ………………………………. 4

4(3) Scape dark, hind tarsi completely white …………………………………..….. tertius
4’ Scape light, hind tarsi with ultimate segment dark ………..……………………… sp. 3

Sp. 1: Scape dark; breadth of decolorized area basal of marginal vein less than length of marginal vein; apical decolorized areas not always fully separated. Contra Costa, Inyo, Marin, San Benito, Stanislaus. (CSCA, RLZC)
Sp. 2: Forewing disc darkened, decolorized apically, but without hyaline spots at apex of venation. Sonoma. (Only 2 specimens, CSCA, RLZC)
Sp. 3: Breadth of decolorized area basal of marginal vein about equal to length of marginal vein, OP sheaths about 0.6x metasoma length. San Bernardino. (Only 1 specimen, UCR)
Sp. 4: Very close to T. kozlovi, but apical edge of scape not as fully rounded. Lassen (1 specimen, RLZC), Yuba (1 specimen, missing head EMEC)

Nearctic species and distibution
americanus (Girault, 1916b): USA (AK, KS, VA)
ashmeadi Noyes & Woolley, 1994: USA (FL)
bakeri (Ashmead, 1900): USA (CO, MO, MT, NM)
brevicollis (Ashmead, 1900): USA (FL, MO)
floridanus Ashmead, 1885: USA (FL)
gracilis (Howard, 1892): USA (FL)
hemipterus (Girault, 1916a): USA (CO)
marilandia (Girault, 1917a): USA (IL, MD)
patro Noyes, 2000: USA (TX)
subapterus (Ashmead, 1900): USA (CO, MT, NM, TX)
tertius Girault, 1917b: USA (CA, UT)
texanus (Howard, 1892): USA (TX)

Remarks
Trjapitzin (2012) presented a key to the females of the world fauna of Tetracnemus, omitting those species known only from males or insufficiently described females, including T. americanus, T. brevicollis, T. floridanus, T. gracilis, T. hemipterus, T. marilandia and T. texanus. Study of specimens in the USNM found the following: T. americanus keys to sp. 1, but the forewing of the former has an apical hyaline patch in addition to those on the anterior and posterior edges (sp. 1 has no such apical patch); only males of T. bakeri, T. brevicauda, T. gracilis and T. texanus were present; T. floridanus keys to sp. 1, but all the funicle segments of the former are greatly flattened and widened, while those of the latter are quadrate and only slightly flattened; the holotype of T. hemipterus has only the meso- and metasomas present (no wings and only one leg) with additional nondescript body parts on a slide; T. marilandia keys to sp. 1, but the former has the body quite flattened dorso-ventrally, very narrow wings (length >5x width), and a hyaline band crossing the width of the wing, while the latter is not flattened, has wider wings, and no complete hyaline band; T. subapterus keys to sp. 4, but the former has a white scape with a length > 6x width, F1 and F2 longer than wide and F3-F6 more or less quadrate, while the latter has a dark scape with a length about 2x width, and all funicle segments transverse and flattened.

References
Ashmead, W.H. 1885. Studies on the North American Chalcididae, with descriptions of new species from Florida. Transactions of the American Entomological Society 12: x-xix.
Ashmead, W.H. 1900. On the genera of the chalcid-flies belonging to the subfamily Encyrtinae. Proceedings of the United States National Museum 22: 323-412.
Girault, A.A. 1916a. New Encyrtidae from North America. Psyche 23: 41-50.
Girault, A.A. 1916b. Descriptiones Hymenopterorum Chalcidoidicorum variorum cum observationibus. III. Entomological News 27: 223-228.
Girault, A.A. 1917a. Chalcidoidea nova Marilandensis. Private publication, Glenndale, Maryland: 2 pp.
Girault, A.A. 1917b. Descriptiones stellarum novarum. Private publication, Glenndale, Maryland: 22 pp.
Howard, L.O. 1892. Insects of the subfamily Encyrtinae with branched antennae. Proceedings of the United States National Museum 15: 361-369.
Noyes, J.S. 2000. Encyrtidae of Costa Rica (Hymenoptera: Chalcidoidea), 1. Memoirs of the American Entomological Institute 62: 355 pp.
Noyes, J.S. & J.B. Woolley. 1994. North American encyrtid fauna (Hymenoptera: Encyrtidae): taxonomic changes and new taxa. Journal of Natural History 28: 1327-1401.
Trjapitzin, V.A. 2012. On the genus Tetracnemus Westwood, 1837 (Hymenoptera: Encyrtidae), with description of a new species from Ethiopia. Russian Journal of Entomology 21: 73-78.