1. Head entirely black or dark chestnut..........................................................................................................2

– Head black with yellow rostrum................................................................................................................4

2. Size larger 13.0- 22.5 mm. Elytra longer, awl-shaped. Clubs of pro- and mesofemora orange-yellow with or without dusky to black fascia. Only tip of mandibles black..................................................................3

– Size smaller 9.0- 10.9 mm. Elytra shorter, wedge-shaped. Femoral clubs may be brownish-orange, but usually entirely dark chestnut to black. Mandibles entirely black. Figs. 5A, 5B............................................................................................................................................................ Isthmiade planifrons Zajciw, 1972

3. Pronotum, all thoracic sternites, scutellum, and basal two-thirds of elytra orange-yellow. Apical two-thirds of elytra, abdomen, and metafemora entirely black. Size larger 20.4-23.7 mm. Fig. 4A............................................................................................................................................... Isthmiade martinsi sp. nov.

– Pronotum always black in part, metasternum and metepisternum mostly or partly orange-red. Elytra almost entirely orange-yellow, urosternites I-III usually red, but abdomen never entirely black. Scutellum black. Size smaller 15.3-18.5 mm. Figs. 3A, 3B................................... Isthmiade ichneumoniformis Bates, 1870

4. Elytra chestnut at apex; longer, 3 times width of humeri, apices truncate and spined. Scutellum black. Pro- and mesofemora without dusky fascia. Figs. 1A, 1B...................... Isthmiade laevicollis Tippmann, 1953

– Elytra entirely yellow; shorter, 2-2.5 time swidth of humeri, apices sharply acuminate. Scutellum yellow. Pro- and mesofemora with dusky fascia. Figs. 2A, 2B.................................. Isthmiade zamalloae sp. nov.