REVISION OF THE NEW WORLD SPECIES OF THE THYANTAE GROUP OF TRISSOLCUS (HYMENOPTERA: SCELIONIDAE)

Abstract The thyantae group of Trissolcus is characterized by the presence of abundant long setae on the metapleuron. All known New World species occur in the Nearctic, viz. T. thyantae Ashmead (eastern USA and Canada), T. occiduus n. sp. (western USA), T. parma n. sp. (widespread), and T. ruidus n. sp. (Arizona, New Mexico). An identification key is provided and all species are described or redescribed. Data on distributions and hosts (Heteroptera: Pentatomidae) are summarized. Résumé Le groupe thyantae du genre Trissolcus est caractérisé par la présence de longues soies sur le metapleure. Toutes les espèces connues du Nouveau Monde se retrouvent dans la région néarctique, soient T. thyantae Ashmead (est des USA et Canada), T. occiduus n. sp. (ouest des USA), T. parma n. sp. (largement répandue) et T. ruidus n. sp. (Arizona, Nouveau-Mexique). On fournit une clé d'identification et toutes les espèces sont décrites ou redécrites. Les données sur leur répartition et leurs hôtes (Heteroptera : Pentatomidae) sont résumées.


I08 THE CANADIAN ENTOMOUX~IST January 1985
This revision is based upon specimens from the following institutions: California State Department of Food and Agriculture, Sacramento, CA (CDFA); Canadian National Collection of Insects, Arachnias and Nematodes, Ottawa, ON (CNC); Los Angeles County Museum, Los Angeles, CA (LACM); New York State Museum, Albany, NY; United States National Museum of Natural History, Washington, DC (USNM).
Wings extending beyond apex of metasoma; radicle yellow to brown, lighter in color than scape; antennae otherwise dark brown to black; femora and tibiae infuscate at least medially .
Hosts: Thyanta custator, Euschistus sp., Nezara viridula (Heteroptera: Pentatomidae) . CANADA: Nova Scotia, Ontario. Remarks. Trissolcus thyantae is most similar to the species described next, T. occiduus, from which it may be distinguished by its narrow malar region, by the lack of a mesopleural carina, and by the dark legs and antennae. Trissolcus thyantae may be separated from the other two Nearctic species of the thyantae group described below (ruidus and parma) by its smooth scutellum and lack of a mesopleural carina.
Trissolcus thyantae appears to be an eastern Nearctic species; the westernmost records are from Columbia, Missouri, and Sault Ste. Marie, Ontario. This distribution does not overlap that known for T. occiduus. Whether these two species are truly allopatric is uncertain; it may be a reflection of collecting effort in the central states and provinces of the USA and Canada.

Trissolcus occiduus new species
Figs. 3 , 4 Length 0.84-1.36 mm (N = 20). Very similar to T. thyantae, differing in the following characters: head, viewed laterally, with malar region strongly expanded posteriorly (Fig. 3); malar region with variably developed, irregular rugulae superimposed on rnicrosculpture; mesopleural carina usually indicated ventrally by fine raised line; usually at least tibiae and scape yellow, appendages generally much lighter in color. Remarks. This species may be distinguished from T. thyantae by the expanded malar region and the presence of a raised mesopleural carina; and from T. parma and T. ruidus by its smooth scutellum, expanded malar region, and lack of any indication of a longitudinal carina on the gena.
I have seen specimens of this species from the western United States only. The name occiduus, from the Latin for western, refers to this distribution. Some specimens from New Mexico have dark appendages and are rather small. Probably as a consequence of size, these are unusual in that the mesopleural carina is absent. More collections are needed to address the question of whether T. occiduus is a species distinct from T. thyantae or whether the variation observed in specimens such as those from New Mexico indicates that there is a transition from typical thyantae to occiduus phenotypes in the central states.
Host Remarks. Trissolcus parma may be distinguished from T. ruidus by the lack of rugulae on the frons (outside of the antennal scrobes) and the lack of longitudinal elements in the sculpture of the posterior portion of the mesoscutum. It may be separated from the two 1 1 I other known Nearctic species of the thyantae group by means of the coriaceous microsculpture present on the scutellum. The name, parma, from the Latin word for a small shield, refers to the scutellum with its characteristic microsculpture.
Trissolcusparma is known from only a few specimens distributed over a broad range, from the Arctic Ocean to the Mexican border of the USA. There is much variability among these specimens: the two from northern Canada are quite small; the specimen from the Northwest Territories has wings that are strongly narrowed and relatively short (just surpassing the apex of the metasoma); the frontal sculpture may show large, well-defined setigerous punctures, or punctures may be lacking altogether. I present here the hypothesis that these specimens belong to a single, widespread, and variable species. Obviously many more collections are needed to resolve this problem.

Trissolcus ruidus new species
Length 1.16-1.29 mm (N = 4). Differs from the preceding species, T. parma, only in the following: irregular rugae superimposed on frontal microsculpture; transverse scrobal sculpture more extensive, extending dorsad of central keel; mesoscutum between notauli with distinct longitudinal elements in sculpture.
Host unknown. Trissolcus ruidus is known only from the southwestern United States. In view of the hypothesized wide range of variability of T. parma it is legitimate to ask whether ruidus is a distinct species, or yet another variant. Within Trissolcus the degree of development of surface sculpture is often correlated with the size of individuals (Masner 1959). However, even the largest specimens of T. parma do not have irregular rugulae on the frons; the effect of size on frontal sculpture is reflected rather in the definition of setigerous punctures and in the depth of incision of the microsculpture. A common theme mentioned in this discussion of all species of the thyantae group is the need for more collecting. It may be difficult to obtain long series of the rarer species until the hosts are discovered.