Homalotylus

May 2018
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KEY A

1 F4 and F5 white, concolorous with F6 and club ………………..………….. pallentipes
1’F4 and F5 dark, concolorous with F1-F3 ………………………………………………. 2

2(1) Club not white, concolorous with (or only slightly lighter than) F1-F4 …………….. 3
2’ Club white ……………………………………………………………………….….… 4

3(2) Mandibles with 2 teeth ………………………………………………….……. similis
3’ Mandibles with 2 teeth and a truncation …………………………………..……… sp. 4

4(2) Scutellum dark, more or less concolorous with scutum ……………………………. 5
4’ Scutellum distinctly lighter than scutum, ranging from yellow to orange to brown ….. 7

5(4) Body completely dark, except club, tarsi and base of tegula white …..………… sp. 2
5’ Body with greater degree of lighter color, at least ventrally ……….………………… 6

6(5) Distal end of stigmal vein almost parallel to leading edge of wing; mandibles with three teeth ……………………………………………………………………….………. terminalis
6’ Distal end of stigmal vein at about a 45° angle to leading edge of wing; mandibles with two teeth (and rudiments of a third) ……………………………………………………….. sp. 1

7(4) Head yellow/orange (vertex may be slightly darkened) with metallic luster weak or absent ……………………………………………………………………………………….….….. affinis
7’ Head dark with distinct bronze/ metallic tinge ………………….………………………. 8

8(7) Ovipositor about 0.5x metasoma length ……………………………….. hyperaspidis
8’ Ovipositor about 0.25x metasoma length ……………………………………….… sp. 3
 

KEY B

1 Ovipositor sheaths not or only slightly protruding …………….……………….…….. 2
1’ Ovipositor sheaths protruding at least 0.25x metasoma length …….…………………. 7

2(1) Mandible with 3 teeth; fuscous band extending across entire forewing ………………………………………………………………………..….… terminalis
2’ Mandible with 2 teeth or 2 teeth plus a truncation; fuscous band fading out before reaching hind edge of forewing ……………………………….……………. 3

3(2) Body and head all black, except club, tarsi and base of tegula white ..………… sp. 2
3’ Body and head with some yellow or orange color ………………….………………… 4

4(3) Club dark, concolorous with at least F1-F3 …………………..……..………………. 5
4’ Club white ……………………………………………………………………..……… 6

5(4) Mandibles with 2 teeth ……………………………………………………..…. similis
5’ Mandibles with 2 teeth and a truncation ………………………………………….. sp. 4

6(5) F4-F5 light ………………………………………………………….……. pallentipes
6’ F4-F5 dark ………………………………………………………………………… sp. 1

7(1) Head yellow/orange …………………………………………..……………….. affinis
7’ Head darker with metallic tinge ………………………………………………………. 8

8(7) Ovipositor sheaths about 0.5x metasoma length …………….………… hyperaspidis
8’ Ovipositor sheaths about 0.25x metasoma length ……………………….…….… sp. 3

Sp. 1 Alameda, Marin, Modoc, Santa Barbara (RLZC), Inyo (EMEC), Los Angeles, Ventura (UCRC), Mono, Stanislaus (UCFC)
Sp. 2 Alameda (RLZC), Lake (EMEC), Nevada, (UCDC), Santa Barbara (SBNHM), Stanislaus (UCFC)
Sp. 3 Glenn, Marin, Santa Clara, Stanislaus (RLZC), Santa Barbara (UCDC), Sonoma (CAS), Los Angeles, Ventura (UCRC). This may turn out to be just a color variant of H. terminalis, but the ovipositor appears to be decidedly longer than H. terminalis.
Sp. 4 Stanislaus (UCFC). Represented by only a single specimen, this may actually not be a Homalotylus species.

Described Nearctic species and distribution

affinis Timberlake, 1919: USA (CA)
albitarsus Gahan, 1910: USA (MD)
brevicauda Timberlake, 1919: MEX (DU)
cockerelli Timberlake, 1919): MEX (GT); USA (TX)
flaminius (Dalman, 1820): USA (LA)
hyperaspidis Timberlake, 1919: USA (CA, UT)
pallentipes (Timberlake, 1919): USA (AZ, CA, MO)
punctifroms Timberlake, 1919: USA (FL)
scymnae (Shimer, 1869): USA (IL)
similis Ashmead, 1887: USA (CA, FL, TX, UT)
teminalis (Say, 1829): CAN (BC); MEX (MR); USA (CA, DL, DC, FL, IL, IN, LA, MD, MA, NJ, NY, PE, SC, TX, UT, WV)

Remarks

            To date, the only comprehensive treatment of Nearctic Homalotylus was contained in Timberlake’s (1919) treatment of the worldwide fauna, wherein desciptions of several new species were based on limited specimens. In this work he separated out Anisotylus partially based on the latter’s two-toothed mandibles (versus three in Homalotylus), and separated three species groups of Homalotylus based first on the length of the ovipositor. Unfortunately, the males and females of the genus are very similar to each other, and distinguishable only by the genitalia, making it extremely difficult to distinguish females of the flaminius group (those with ovipositor not protruding) from all males. Anisotylus has since been synonymized with Homalotylus, so it seemed natural to me to use the difference in mandibular structure to help distinguish those species, but counting mandibular teeth is another difficult chore for old specimens whose mouthparts are not separated. In his keys, Timberlake also relied on the length:width ratios of the head, but the minute differences he cited for this feature do not seem clear cut to me. I first constructed a key whose initial couplets were based upon the differences in ovipositor and mandibular structure that Timberlake relied on. But given the difficulty in distinguishing the sex and counting mandibles, it proved very hard to use. So I produced another key based primarily on color differences. Ultimately this second key may prove to be of little avail should the color variation within species prove to be high (or for non-California species), but at least initially it seems to be a fairly easy way to distinguish our species. Therefore, I have included both keys: KEY A is based largely on color, and KEY B initially separates species by ovipositor length and mandibular dentition. In my collection are two males (one from Stanislaus County and one from Tehama County) that appear referable to Homalotylus, but appear to represent two additional species. There is also a series from Arizona (UCRC) that appear intermediate between H. affinis and my Homalotylus sp. 3. Trjapitzin & Ruiz Cancino (1998) presented a key to species from the New World. Ashmead (1900) synonymized Eutelus scymnae under H. terminalis, but Timberlake (1919:57) considered this was done “on apparently insufficient evidence”, so I am retaining it here as a good species pro tem. Specimens from the USNM of H. cockerelli key to H. hyperaspidis in Key A, while H. albitarsus almost keys to H. pallentipes (the former has the F4 partially dark). Additionally, H. brevicauda keys to sp. 3 in key A, but the former has F1 quadrate of slightly longer than wide, while in the latter, F1 is definitely longer (1.5x) than wide, and H. punctifrons keys to H. hyperaspidis in Key B, while in Key A it matches nothing (F5 is all or mostly light).

 

References

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.

Dalman, J.W. 1820. Försök till Uppställning af Insect-familjen Pteromalini, I synnerhet med afseen de på de I Sverige funne Arter (Fortsättning). Kungliga Svenska Vetenskapsakademiens Handlingar 41: 123-174, 177-182, 340-385.

Gahan, A.B. 1910. Four new species of Hymenoptera. Chalcidoidea, Encyrtidae. Canadian Entomologist 42: 205-208.

Noyes. J.S. 2010. Encyrtidae of Costa Rica (Hymenoptera: Chalcidoidea), 3. Memoirs of the American Entomological Institute 84: 848 pp.

Say, T. 1829. Descriptions of a new species of Hymenoptera of the United States. Contributions of the Maclurian Lyceum to the Arts and Sciences, Philadelphia 1: 67-83.

Shimer, H. 1869. Notes on Chermes pinicorticis (“White-pine louse.”). Transactions of the American Entomological Society 2: 383-385.

Timberlake, P.H. 1919. Revision of the parasitic chalcidoid flies of the genera Homalotylus and Isodromus Howard, with descriptions of two closely related genera. Proceedings of the United States National Museum 56: 133-194.

Trjapitzin, V.A. & Ruiz Cancino, E. 1998 (1997). Homalotylus terminalis (Say) (Hymenoptera: Chalcidoidea: Encyrtidae), un parasitoide de coccinélidos (Coleoptera: Coccinellidae) en el Estado de Morelos, México, Ceiba 38: 157-160.