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 WechslerPhoto 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.
Mandible morphology
Head modifications
Female antennae
Male antennae
Anterior propodeal process
Propodeal carination
Propodeal bump
Polished "boss"
Amblypygy vs oxypygy
Postpetiole sculpture
Gastrocoelus and thyridium
Color characters
Antennal banding
Hind tibia banding
Median field
clypeus usually flat with straight ventral margin (convex in
Platylabini, Trogus, Hoplismenus and a
few other genera)
areolet usually pentagonal (infrequently quadrangular
or open posteriorly)
metasomal tergite 1 with spiracle past midpoint of segment
metasomal tergite 2 usually with gastrocoelus
ovipositor short (usually not projecting past metasomal apex)
male flagellum often with tyloids or sometimes bristleridges
FILTER MENU
Mesopleuron color
Wing
Metasoma
Region
State
Anterior transverse carina of propodeum
Occipital carina
Epicnemial carina
Umbo
Ramellus
Sex
Genus
1. Propodeal spiracle circular and anterior margin of propodeum with
medial protuberance. Small in size and clypeus usually weakly to
moderately convex
. . . . 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
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)
- 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)
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)
- Habitus and color as in image below (i.e. metasoma yellow with
black apex) . . . . Neamblymorpha
milva (Northeastern North America)
- 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
- 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 . . . . 4
- Epistomal suture at least weakly indicated. Mandibles usually moderately narrow with
dorsal tooth distinctly longer than ventral tooth . . . 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 not produced 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
- 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
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)
- 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)
- 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
- 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.
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)
- 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
Claridge, B. (2021). Revision
of Nearctic Heterischnus
Wesmael, 1859 (Hymenoptera, Ichneumonidae, Ichneumoninae,
Phaeogenini). Journal of Hymenoptera Research,
85, 57–79. https://doi.org/10.3897/jhr.85.67792
