Thyreodon rivinae, PORTER, 1980

Gauld, Ian D. & Janzen, Daniel H., 2004, The systematics and biology of the Costa Rican species of parasitic wasps in the Thyreodon genus-group (Hymenoptera: Ichneumonidae), Zoological Journal of the Linnean Society 141 (3), pp. 297-351 : 333-334

16. THYREODON RIVINAE PORTER

Thyreodon rivinae Porter, 1980: 243 . Holotype ♀, USA, TEXAS (FSCA) [examined].

Athyreodon rivinae (Porter) Porter, 1989: 298 .

Fore wing length 16.5–18.2 mm; clypeus weakly convex, with margin flared outwards, with apex pointed medially; malar space about 0.1 times basal mandibular width; maxillary palp long with second palpomere strongly broadened and flattened; lower face centrally finely punctate; frons swollen between antennal sockets, with a weak to moderately sharp median vertical ridge, and with a low carina extending from outer rim of antennal sockets upwards, close to and parallel with eye margin; frons centrally rather smooth; ocelli very large, the lateral ocellus contiguous with eye; head in dorsal view with gena rather evenly rounded behind eye, occipital carina strong, its lower end only weakly raised, not reaching hypostomal carina; antenna setaceous, with 51–53 flagellomeres, the 20th subquadrate, 0.9–1.0 times as long as broad, the subapical ones with setae which are slightly shorter than the diameter of the flagellomere. Pronotum short with anterior margin moderately strongly and broadly reflexed, and with posterior margin centrally swollen, slightly angular, separated from the anterior margin by a broad U-shaped groove ( Fig. 24 ); epomia absent; propleuron very sparsely punctate, with lower corner rounded, peripherally not impressed; mesoscutum finely punctate, with sharply impressed, deep notauli which are close together posteriorly, inner anterior margin of notaulus unspecialized; scuto-scutellar groove very deep, laterally margined by a strongly raised, simple, thickened carina; scutellum finely punctate, weakly convex; mesopleuron finely punctate, without a sharp sternaular impression; metapleuron finely punctate, sometimes with a few obscure diagonal ridges; propodeum laterally slightly flattened, reticulate with interstices coriaceous, with a low rounded ridge above and behind the spiracle; propodeum posterodorsally rugose-reticulate, with transverse rugae posterolaterally, centrally with a very shallow median longitudinal impression. Fore leg of female slender, with coxa without a rounded protuberance behind trochanteral insertion; 5th tarsomere 0.4–0.5 times as long as the preceding two tarsomeres, with tarsal claw quite short, with fine, close pectinae; hind coxa in profile moderately large, its hind end projecting slightly beyond level of hind end of propodeum; hind femur slender, about 6 times as long as maximally deep. Fore wing with abscissa of Cu 1a between Cu 1b and 2 m-cu 1.1–1.2 times as long as abscissa of Cu 1 between cu-a and 1 m-cu. Metasoma with tergite I slender, anteriorly subcylindrical; tergite II, in lateral view, 2.1–2.3 times as long as posteriorly deep. Male unknown.

A blackish brown species with flagellum bright yellow; wings basally and apically blackish infumate, centrally almost hyaline.

Remarks: Structurally Thyreodon rivinae closely resembles T. maculipennis . Both lack strong interantennal carinae, and an epomia, and both have the fore leg slender with the 5th tarsomere slightly shorter than the 3rd. Both also have the fore wing peripherally dark but centrally hyaline. T. rivinae differs most conspicuously from T. maculipennis in having the posterior ocelli contiguous with the eyes, and the flagellum yellow (orange in living specimens).

Biological notes: Although Thyreodon rivinae is common at the lights in ACG dry forest from late May to early July (and almost no others have been collected, suggesting strong univoltism) ( Fig. 65 ), none has been reared from thousands of sphingid caterpillars and many tens of species of sphingids reared from the ACG dry forest.

Either T. rivinae probably parasitizes one of the few species of Sphingidae whose caterpillar has not yet been encountered or it parasitizes one of the few species not yet frequently sampled. The obvious candidate for the latter is Erinnyis obscura , only ten caterpillars of which have been reared. One of these was parasitized by a small Thyreodon that died in its cocoon [94-SRNP-3289]. E. obscura feeds on herbaceous asclepiadaceous vines in insolated early successional stages, a distinctive common microhabitat from which no sphingid-parasitizing species of Thyreodon has been reared.

Material examined: Holotype ♀, USA, TEXAS, Hidalgo County, Bentsen Rio Grande Valley State Park , vii.1979 (Porter) ( FSCA).

Non-type material: COSTA RICA: Guanacaste Prov.: 2 ♀ , 3 km E Cuajiniquil , 300 m, vi.1992 (Parataxonomists) ( INBio ); 2 ♀ , Guanacaste National Park, Estacion Murcielago , 8 km SW Cuajiniquil, 100 m, vi.1992 (Parataxonomists) ( INBio ); 4 ♀ , Guanacaste National Park, Finca Jenny , 30 km N Liberia, 240 m, vi.1991, vi–vii.1992, vii.1993 (Espinoza & Araya) ( INBio ); 2 ♀ , Guanacaste National Park, Sector Santa Rosa , caught as adult but listed in data-base as 99-SRNP-8560, 99- SRNP-9078 (Franco) ( JHVC); 2 ♀ , Lomas Barbudal , 30 m, vii.1991 (Chavarria) ( INBio ); 2 ♀ , Santa Rosa National Park , 300 m, vi.1980, vi.1984 (Janzen & Hallwachs) ( BMNH); 23 ♀ , same locality, v–vi.1985 (Janzen & Hallwachs) ( INBio ); 9 ♀ , same locality, vi.1985, vii.1986, vi.1989 (Gauld) ( BMNH); 10 ♀ , Santa Rosa National Park , 300 m, ii.1992, vi–vii.1992 (Parataxonomists) ( INBio ) .

Figures

Figure 65. The total numbers of individuals of Thyreodon rivinae collected at light by month between 1985 and 1992 in Sector Santa Rosa of the ACG compared with the monthly percentage of the annual rainfall.

Figures 21–26. SEM photographs of Thyreodon spp., pronotum, lateral; 21, T. whitfieldi; 22, T. laticinctus; 23, T. darlingi; 24, T. rivinae; 25, T. morosus; 26, T. walkerae.