Subfamily Ichneumoninae



Ichneumoninae is the largest ichneumonid subfamily with ~4,300 species in 437 genera. In North America alone, there are around 715 described species, with likely several hundred more awaiting formal description. Ichneumonines are among the most striking ichneumonids due to the striking coloration of many species. The most commonly encountered species are in the sexually dimorphic genera like Ichneumon and Diphyus. Males of these genera are often apparent mimics of stinging wasps (Aculeata) and can be found flying above vegetation frenetically searching for mates. Females tend toward more drab colors like brownish-red and black and are spend more time searching around vegetation for hosts.

Photo by Doug Wechsler
Photo by Denis Doucet


All ichneumonines are endoparasitoids of lepidopterans and oviposit into the host larva or pupae and almost always emerge from the host pupa. The only exception is Colpognathus which emerges from the mummified remains of the host final instar larva. Unlike the many ichneumonid groups that oviposit into their concealed hosts with the aid of a long ovipostior, ichneumonine females gain direct access to their hosts prior to oviposition. This often requires digging through soil and leaflitter or crawling under bark crevices and through plant stems. Species in which the females have a rounded or blunted metasomal apex (=amblypygous) always attack larvae and are true koinobionts that oviposit into earlier instar larvae. Those with a sharper metasimal apex with an exposed ovipositor (=oxypygous) may either attack larvae or pupae but probably most commonly oviposit into prepupal larvae or fresh pupae. Ichneumonines are somewhat unusual in that many genera overwinter as adult females in a variety of hibernacula like tufts of grass, beneath bark, and under moss.

Photo by Julian F.


For published keys, see Gerd Heinrich's series revising the Ichneumoninae "Stenopneusticae" of the Northeastern region, which covers all tribes besides Phaeogenini (=Cyclopneusticae). Heinrich's keys are critical for identifying most described species. Although low on figures, the species keys work well and are normally based on easy-to-view characters like color. However, some couplets do come down to a comparison between two species, which is impossible to evaluate without specimens of both species at hand. The generic key is somewhat more difficult to use as it relies on characters that can be difficult to interpret (e.g., development of the gastrocoelus and thyridium).

Another confounding factor for beginners with using Heinrich's generic key is that recently there has been a massive simplification of ichneumonine tribes (Santos et al. 2021) such that in North America there are only Ichneumonini, Phaeogenini, and Platylabini. Acanthojoppini, Listrodromini, Protichneumonini, and Trogini are no longer valid and have been synonymized with Ichneumonini.

For Florida and other states in the southeastern U.S., see Heinrich's (1977) "Ichneumoninae of Florida and neighboring states: (Hymneoptera, Ichneumonidae, subfamily Ichneumoninae)". This work treats all ichneumonines (including Phaeogenini) in Florida and a random, partial assortment of those occurring in surrounding states. It is authoritative for Florida (excluding a few undescribed species), but by no means for the other southeastern states, where we know much less.

For a modern and thorough treatment of the Platylabini of the southeastern U.S., see Dal Pos et al. (2022).

Unfortunately, identifying ichneumonines to species outside of the eastern U.S. and Canada is extremely difficult due to a lack of taxonomic work. This is particularly acute in the western U.S., which is massively undercollected and where the majority of species are undescribed.

Head

Bristle ridges

The majority of ichneumonine males have simple filiform antennae where each individual flagellomere is roughly cylindrical. Bristle ridges are modifications of the flagellomeres in which nodose transverse ridges are present along the venter of each flagellomere, complete with a few projecting bristles. The development of bristle ridges occurs along a spectrum. Cratichneumon and Coelichneumon both have somewhat weak bristle ridges, while in Melanichneumon they are even more defined. Overall, bristle ridges are less common in temperate taxa than in tropical ones but strongly developed bristle ridges can be seen in Carinodes, Plagiotrypes, Setanta, Tricholabus, and Trogomorpha, which occur in the Nearctic and Neotropics.

Bristle ridges absent – no trace of bristle ridges.

Bristle ridges weak – bristle ridges are visible but not particularly acute or prominent.

Bristle ridges moderately developed – bristle ridges intermediate between weak and strong

Bristle ridges strong – bristle ridges strongly nodose.

Tyloids

Tyloids are raised areas on the dorsolateral surface of the male flagellomeres. The size and shape of the tyloids vary considerably as well as which flagellomeres they span. Regarding size, tyloids vary from being minute, barely visible dots to occupying the entire length and width of the dorsolateral surface of the flagellomere. The shape varies along with their size, but is typically characterized as being either bacilliform (rod-like), linear, or ovoid. The majority of male ichneumonines posess tyloids but some do not. Both the presence/ absence and which flagellomere the tyloids begin on are important generic characters. More broadly, the morphology of tyloids is typicall species specific and can be critical in separating males of otherwise similar species.

Tyloids absent

Tyloids medium-sized

Tyloids enlarged

Female flagellum

*****

Filiform – ***.

Bristle-shaped – ***.

Female basal flagellomeres

*****

Basal flagellomeres stout – less than 1.5x as wide as longp>

Basal flagellomeres moderate length – ***.

Basal flagellomeres elongate – greater than 3 times as wide as long.

Mandible

Mandible bidentate, moderately narrow – ****

Mandible bidentate, wide, with subequal teeth – ****

Mandible unidentate, shovel-shaped

Mesosoma

Juxtacoxal carina

*****

– ***.

Median process on anterior margin of propodeum

*****

– ***.

Wings

Areolet

*****

– ***.

Legs

Coxal modifications

There are two types of modifications of the female hind coxa: a scopa and various types of projections that vary from being dentate, lobe-like, and carinate. These modifications are apparently used as aids in oviposition but the specifics are not entirely clear. A scopa is a dense patch of setae. Only some female Ichneumonini possess a scopa. In exceptional cases, a scopa may also be present on the mid coxa. The coxal projections are unique to Phaeogenini (except for Stenichneumon culpator, at least in the Nearctic). Within genera, the presence or absence of a scopa or projection can be variable but the size and shape of a modification can be an important species-specific character.

Scopa absent – no apparent trace of a scopa.

Scopa small – scopa present but occupying a small portion of the hind coxa.

Scopa medium-sized – scopa intermediate in size.

Scopa large –

Metasoma

Postpetiole surface sculpture

The surface sculpture of the postpetiole (the wider, posterior section of the first metasomal tergite) is a major character that separates genera and even larger genus-groups. The three primarily states are smooth/granulate, densely punctate, and striate, though intermediates between these states occur.

Smooth – postpetiole primarily free of punctation, striation, or rugosity. Sometimes with a few punctures laterally. Often, taxonomists group a smooth and granulate postpetiole together.

Densely punctate – distinct punctures covering most of the postpetiole of the first metasomal segment.

Longitudinally striate – linear striations ....

Rugulose – ****

Thyridium

The thyridium is a matt area on the anterior of the second metasomal tergite. It should not be confused with the pseudothyridium on the posterior half of the second metasomal tergite. The thyridium varies from minute as in Diphyus to nearly spanning the entire width of the tergite as in Stenichneumon. The width is usually discussed in relation to the interthyridial width meaning the interval between both thyridia. The size of the thyridium is usually shared among all members of a genus though there are exceptions like in Ichneumon where it varies from narrower than inter thy

Thyridium absent – there is no trace of the thyridium.

Thyridium small – thyridium present but small and scar-like.

Gastrocoelus

*****

Gastrocoelus absent – no depression visible on anterior of second metasomal tergite.

Gastrocoelus shallow – ****.

Gastrocoelus moderately impressed – ****.

Gastrocoelus deeply impressed – ****.

Female metasomal apex

The female metasomal apex (posterior end of the metasoma) varies between oxypygous and amblypygous, roughly meaning sharp vs. blunt, respectively. This is a major character used in Ichenumoninae taxonomy but it can be difficult to interpret, especially given the variation in position in mounted specimens and the fact that there is a spectrum from oxypygy to amblypygy with an intermediate state of "semi-amblypygy". Several characters accompany the two extremes: amblypygy associated with a longer hypopygium significantly concealing the ovipositor with the latter being narrow and needle-like, while in oxypygous females the hypopygium is shorter and the ovipositor more robust. While defining

Oxypygous – female metasomal apex with hypopygium short leaving ovipositor largely exposed. In dorsal view, metasomal apex appearing sharp or pointed.

Amblypygous – female metasomal apex with hypopygium longer, partially or almost entirely concealing ovipositor. In dorsal view, metasomal apex appearing rounded or blunted.

semi-amblypygous – female metasomal apex intermediate between oxy- and amblypygous.

  • clypeus usually flat with straight ventral margin (convex in Platylabini, Trogus, Hoplismenus and a few other genera)
  • areolet usually pentagonal (infrequently quadrangular or open apically)
  • metasomal tergite 1 with spiracle posterior to segment midpoint
  • metasomal tergite 2 usually with gastrocoelus
  • ovipositor short (usually not projecting significantly past metasomal apex)
  • male flagellum often with tyloids or sometimes bristleridges

    1. Propodeal spiracle circular and anterior margin of propodeum with medial protuberance. Small in size and clypeus usually weakly to moderately convex . . . . Phaeogenini
    Phaeogenini

    - Propodeal spiracle almost always linear or if propodeal spiracle circular (Cyclolabus, Linycus and Neolinycus), then without medial protuberance on anterior margin of propodeum. Varying from small to large, though almost always larger than Phaeogenini. Most with flat clypeus (Platylabini, Hoplismenus, and Trogus with convex clypeus) . . . . 2
    Phaeogenini

    2. Petiole (narrowed anterior area of metasomal segment 1) wider than high in cross section; or, if petiole about as high as wide, then propodeum essentially reticulate (irregularly rugose) and female metasomal apex oxypygous (Apaeleticus, moderately rare). Clypeus usually strongly convex, sometimes weakly convex. Female metasomal apex always amblypygous . . . . Platylabini (excluding Probolus)
    Platylabini

    - Petiole in cross section approximately square or higher than wide. Clypeus usually flat though strongly convex in a minority of genera (e.g. Hoplismenus, Trogus). Female metasomal apex oxypygous or amblypygous . . . . Ichneumonini and Probolus (Platylabini)
    Ichneumonini




The following generic key is still in development. It is meant to be maximally useful for non-experts and thus focuses on more easily visible characters.



1. Hind leg black except for brownish-red femur. Habitus as in image below . . . . Limonethe maurator (common in open fields)
Limonethe

- Habitus and color as in image below (i.e., metasoma yellow with black apex) . . . . Neamblymorpha milva (Northeastern North America)

Neamblymorpha

- Habitus and color as in image blow (i.e. T1-2 brownish-red and T3-7 black, female with yellow antennal banding, male without antennal banding) . . . . Tmetogaster nubilipennis



- Hind leg otherwise. Habitus and color various . . . . 2

2. Metasomal tergites "blocky" and clypeus convex . . . . Trogus

- Metasomal tergites normal or clypeus flat . . . . 3

3. Epistomal suture completely absent such that clypeus and supraclypeal area form a continuous plane. Mandibles short, broad and with subequal teeth. Propodeum short with areola wider than long . . . . 4

- Epistomal suture at least weakly indicated. Mandibles usually moderately narrow with dorsal tooth distinctly longer than ventral tooth. Propodeum usually of moderate length usually with areola as wide as long or longer than wide (infrequently with areola wider than long) . . . 5

4. . . . . Anisobas

- . . . . Neotypus

5. Areolet diamond-shaped or irregularly pentagonal. Large species. . . . 6 (Callojoppa genus group)

- Areolet pentagonal. Usually medium-sized to small (except Protichneumon and Ichneumon devinctor) . . . . 9

6. . . . .

-

7. . . . .

-

8. . . . .

-

9. Propodeum with spine-like apophyses . . . . 10

- Propodeal apophyses absent or at most dentate . . . . 14

11. Mandible sickle-shaped and unidentate. Apical tergites of female with anterior unsclerotized. Coloration as in habitus image below . . . . Plagiotrypes concinnus

Plagiotrypes

- Mandible bidentate. Apical tergites of female fully sclerotized. Coloration various . . . . 12

12. Propodeal apophyses elongated. Clypeus convex. Overall color various but never mostly brownish-red . . . Hoplismenus

- Propodeal apophyses small. Clypeus flat or nearly so. Overall color brownish-red . . . . 13

13. Anterior margin of propodeum with medial process. . . . Rubicundiella

- Anterior margin of propodeum without medial process. . . . Hemihoplis

14. Anterior margin of propodeum with medial process. Postpetiole often densely punctate. . . . 15

- Anterior margin of propodeum without medial process. Postpetiole usually longitudinally striate, granulate, or smooth (infrequently punctate) . . . . 26

15. Areola with medial carina. . . Carinodes (rare, present only in Florida, Texas, and Arizona)

- Areola without medial carina. . . . 16

16. Females . . . . 17

- Males . . . . 22

17. Flagellum greatly widened and flattened subapically and sharpely tapering apically. . . . Melanichneumon

- Female flagellum weakly widened and flattened subapically. Areola of male usually nearly straight posteriorly 18

18. Postpetiole primarily smooth. . . . Vulgichneumon

- Postpetiole densely, coarsely punctate. . . . 19

19. Thyridium and gastrocoelus wide (interthyridial width narrower than thyridium). . . . Stenobarichneumon

- Thyridium and gastrocoelus narrow (narrower than interthyridial width). . . . 20

20. Clypeus extremely short and wide. . . . Rictichneumon (rare)
Richtichneumon

- Clypeus of normal length and width. . . . 20

20. Gastrocoelus more deeply impressed than alternative. Color usually with extensive yellow areas or primarily black. Metasomal apex normally marked yellowish-white or yellow. . . . Virgichneumon

- Gastrocoelus more weakly impressed. Color usually brownish-red and metasomal apex not marked yellowish-white or yellow. . . . Barichneumon

21. Flagellum with strongly developed bristle ridges. . . . 22

- Flagellum without wor with poorly developed bristle ridges . . . . 23

22. Postpetiole densely, coarsely punctate. Areola wide and posteriorly impressed. Gastrocoelus and thyridium close to anterior margin of T2. . . . Melanichneumon

- Postpetiole predominantly smooth, sometimes with weak longitudinal striation. Gastrocoelus and thyridium pushed back slightly from anterior margin of T2 . . . Vulgichneumon

23. Clypeus extremely short and wide. . . . Rictichneumon (rare)
Richtichneumon

- Clypeus of normal dimensions. . . . 24

24. Gastrocoelus and thyridium wide (wider than interthyridial width). Medial paraocular area usually broadly yellowish-white. . . . Stenobarichneumon

- Gastrocoelus and thyridium narrow (narrower than interthyridial width). Medial paraocular area same color as remainder of head. . . . 25

25. . . . Barichneumon

- . . . . Virgichneumon

26. Postpetiole granulate . . . . 27

-Postpetiole smooth, longitudinally striate, or punctate. . . .

27. Ovipositor long (projecting past metasomal apex). . . . Crypteffigies

- Ovipositor short (not projecting past metasomal apex) . . . . 28

28. Female metasomal apex amblypygous. Propodeal carinae poorly developed. . . . Anisopygus

- Female metasomal apex oxypygous Propodeal carinae well-developed.(except for 2 rare unplaced amblypygous genera from Wyoming and Utah; except in these genera coloration either primarily brownish-red or yellowish-white and brownish-red; extremely rare). . . . . 29

29. Gastrocoelus and thyridium wide (wider than interthyridial width). . . . 30

- Gastrocoelus and thyridium narrow (narrower than interthyridial width). . . . 31

30. Mesonotum smooth (polished). Head in frontal view nearly paralell-sided (not significantly tapering ventrally). . . . Homotherus

- Mesonotum granulate. Head in frontal view tapering ventrally. . . . Aoplus

31. Pseudoplatylabus



32. . . . Platylabops

- . . . 33

33. Cratichneumon

- Eupalamus

34. Propodeum sloping (without distinct dorsal and posterior faces). Second lateral area long. . . . Often with iridescent coloration.

- Propodeum broken (with distinct dorsal and posterior faces). Second lateral area normal length . . . . 35

35. Metasoma brownish-red. Male head primarily yellowish-white. . . . Protichneumon

- Metasoma black or iridescent blue. Male head primarily black . . . . 36.

36 Metasoma with tergites 2-3 brownish-yellow. . . . . Amblyjoppa

Amblyjoppa

- . . . . 37

37. . . . Protopelmus

- . . . . Coelichneumonops

38. Postpetiole



1. Mandible unidentate and sickle-shaped . . . . 2

- Mandible bidentate (ventral tooth at least represented by small notch) . . . . 3

2. Gastrocoeli and thyridia wider than interthyridial width. Scutellum strongly raised above postscutellum . . . . Heterischnus (present throughout North America)

- Gastrocoeli and thyridia narrow and subobsolete. Scutellum nearly flat and not significantly raised above postscutellum . . . . Stenodontus (present at higher latitudes, high elevation sites in the southeastern U.S., and in southeastern Arizona and Mexico)

3. 3rs-m of fore wing absent (areolet open apically) . . . . Epitomus (several undescribed species present in North America despite genus unrecorded from Nearctic)

- 3rs-m of fore wing present (areolet pentagonal) . . . . 4

4. Gastrocoeli and thyridia absent . . . . 5

- Gastrocoeli and thyridia present . . . . 8

5. Areola heart-shaped. Overall color usually black . . . . Dicaelotus

- Areola coffin-shaped or rectangular. Predominantly brownish-red, . . . . 6

6. Female metasomal apex amblypygous. Female mandible enlarged. . . . Colpognathus

- Female metasomal apex oxypygous. Female mandible of normal width. . . . 7

7. Body elongated. Surface sculpture overall granulate. . . . Eparces (Northeastern U.S. and costal regions of south GA to south FL).



- Body of normal dimensions. Surface sculpture variable but with at least moderate punctation . . . . Centeterus (throughout North America)

8. Postpetiole coarsely, densely punctate . . . . Herpestomus

- Postpetiole varing from smooth to longitudinally rugulose. . . . 9

9. Gastrocoeli and thyridia narrow (thyridium narrower than interthyridial width). Female with 7th tergite constricted anteriorly. Mandible with ventral tooth reduced to small notch. . . . Jethsura

- Gastrocoeli and thyridia wide (single thyridium greater than interthyridial width). Mandible with ventral tooth not significantly reduced. . . . 10

10. Female with large projection on ventral surface of hind coxa formed by the juncture of two carinae. Ventral surface of clypeus roughened medially. . . . . Dirophanes

- Female with or without hind coxal projection but if present then never carinate. Ventral surface of clypeus either smooth or punctate but never roughened.i. . . . 11

11. Ventral margin of clypeus wide and punctate. . . . Phaeogenes - Ventral margin of clypeus smooth and always without punctures . . . 12 12. Carina immediately behind mandible strongly elevated resulting in a deeply excavated area posterior to mandible. Clypeus sharply impressed. Scutellum flat (not raised above postscutellum). Head wide and transverse . . . Aethecerus

- Scutellum usually at least weakly convex and partially raised above postscutellum (some Tycherus with a entirely flat scutellum). Head normally about as wide as long (some Tycherus with wide transverse heads). . . . 12

13. Head strongly convex anteriorly. Epistomal suture absent (supraclypeal area and clypeus forming smooth uninterrupted surface). Ventral margin of of clypeus sharply impressed (resulting in what appears to be a double margin) . . . Diadromus

- Head weakly convex anteriorly. Epistomal suture present. Ventral margin of clypeus variable not impressed. . . . 13

14. Ovipositor projecting significantly past metasomal apex. Surface scultpure granulate and impunctate. . . . Tereberella (rare)

- Ovipositor not significantly projecting past metasomal apex. Surface sculpture at least partially punctate. . . .14

15 . . . . Phaeogenes

- . . . . Tycherus

Genera by species richness

Most species-rich genera

Top genera by species richness.

Regional species richness

Species described per decade

Junior synonyms described per decade

Cumulative species described

Top taxonomic authors

Authors ranked by number of valid species described.

Nomenclatural flux

For each genus, species originally described there (blue) vs. transferred in from another genus (orange). Percentage shown inside orange bar when space allows.

Synonymy by genus

Valid species vs. synonyms per genus. Color indicates synonymy ratio (blue = low, red = high). Hover a point for details.