This is a long and fairly exhaustive post, but each section includes distribution data so you can easily search for species that might occur in your area. For a more detail-oriented treatment of these insects, check out my recent open-access (=free download) field guide, although it's somewhat outdated only 10 months later.
Section 1: Introduction
Section 2: Microseridinae Gall Wasps
Section 3: Lettuce Gall Wasps
Section 4: Silphium Gall Wasps
Section 5: Hawkweed Gall Wasps
Section 6: Other Assorted Gall Wasps
Collecting and Rearing Herb Gall Wasps
Key Targets for Collection
Many of you are likely familiar with oak galls induced by wasps of the tribe Cynipini. However, gall wasps induce galls on a vast array of host plants, and those other than oak gall wasps have not received much study in recent years (or ever!). My focus is on gall wasps associated with herbaceous plants (i.e., often short lived plants that are not trees or shrubs). In North America, cynipid galls on herbaceous plants are induced by species belonging to three tribes: Aulacideini (my primary focus), Diastrophini (these primarily gall Rubus and Potentilla), and Phanacidini (two known species, both introduced from Europe).
As published in my recent catalogue of North American gall wasps, there are 21 species of the tribe Aulacideini known in North America. However, very early on in my study, it was immediately obvious that our current knowledge only scratched the surface. Thus far, I've encountered as many as 50 total species of Aulacideini in North America, many of which are undescribed species (i.e., new to science) that I intend to describe. In addition to many new species, the two genera of Aulacideini present in North America (Antistrophus and Aulacidea) are polyphyletic, meaning that they contain species representing several different lineages that are not closely related. Because of this, many species of North American herb gall wasps will need to be moved to new genera that will be established as a result of my studies. All in all, there are clearly many classification problems in this group that I am aiming to resolve with my studies.
This post will be split into several sections based on the host plant taxon. Each section will begin with a table outlining the known gall wasps on that host taxon, including the following information:
Please peruse this list to learn about progress on my research, and what material you might be able to collect to help understand the biodiversity of this group of insects! If you have any questions about these insects, or galls and wasps in general, do feel free to comment below or message me otherwise! At the end of the post, I have included some information on collecting and rearing herb gall wasps if you'd be so kind as to collect some material on my behalf. Anything listed in this post as not sequenced or without adults known is of high priority for collection!
Microseridinae Gall Wasps
The species in this group all induce galls on a subgroup of the lettuce tribe (Asteraceae: Cichorieae: Microseridinae). These wasps appear to form a monophyletic group (i.e., a “good group” that contains an ancestor and all of its descendants) and appear to comprise three true genera.
Species | Distribution | Host plant | Galled organ | Gall shape | Adults? | Sequenced? |
---|---|---|---|---|---|---|
Antistrophus pisum | Midwestern and Western US + adjacent Canada | Lygodesmia juncea | Stems | Pea-shaped | Yes | Yes |
Antistrophus sp. nov. | Midwestern and Western US + adjacent Canada | Lygodesmia juncea | Stems | Spindle | Yes | Yes |
Antistrophus sp. nov. | Midwestern and Western US + adjacent Canada | Lygodesmia juncea | Basal stems (usually below soil!) | Amorphous | Yes | Yes |
Antistrophus microseris | California; one record from Arizona | Microseris douglasii | Stems | Spindle | Yes | Yes |
Antistrophus sp. nov.? | California | Microseris paludosa | Stems | Spindle | No | No |
Antistrophus sp. nov. | Southcentral US; Texas and Oklahoma | Pyrrhopappus grandiflorus | Stems | Cluster/spindle | Yes | Yes |
Antistrophus sp. nov.? | California | Uropappus lindleyi | Stems | Cluster/spindle | No | No |
Gall wasps on plants belonging to the Microseridinae appear to comprise a fairly diverse group. It is likely that undescribed species exist on other species of Microseris (of which there are many), as well as other genera in this group such as Agoseris. There are also several additional species of Lygodesmia in the Midwestern and Southern US that could be hosts for undescribed gall wasps.
At this time, it is unclear whether galls found on Microseris paludosa and Uropappus lindleyi are new host plant records for Antistrophus microseris or if these galls truly represent new species. Given the restrictive host plant range of most herb gall wasps, it is quite likely that these are new species, but DNA sequences and examination of adult wasps would be necessary to confirm this.
Lettuce Gall Wasps
Species in this group all belong to the genus Aulacidea, the most diverse herb gall wasp genus comprising more than 40 species known in North America and Eurasia. Aulacidea is in desperate need of reclassification, as the vast majority of species classified here do not belong. In fact, only the species of gall wasps classified in Group B are properly classified in this genus!
Species | Distribution | Host plant | Galled organ | Gall shape | Adults? | Sequenced? |
---|---|---|---|---|---|---|
Aulacidea podagrae | Widespread in Eastern and Midwestern US | Lactuca biennis | Stems | Variable; cluster- or node-like | Yes | Yes |
Aulacidea sp. nov. | Widespread in Eastern US | Lactuca biennis | Stems | Cryptic cells hidden in stem tissue | Yes | Yes |
Aulacidea abdita | Eastern US and Canada? | Lactuca canadensis??? | Stems | Cryptic cells hidden in stem tissue | Yes | No |
Aulacidea harringtoni | Widespread in Eastern and Midwestern US | Lactuca canadensis | Stems | Cryptic cells hidden in stem tissue | Yes | Yes |
Aulacidea tumida | Widespread in Eastern and Midwestern US | Lactuca canadensis | Stems | Variable; usually clavate or spindle-like | Yes | Yes |
The lettuce gall wasps comprise several species of host-specific wasps that induce either visible or cryptic (hidden) galls. Thus far, I have confirmed the identity of lettuce gall wasps on only two species of lettuce, Canadian lettuce (Lactuca candensis) and tall blue lettuce (L. biennis), although there are several other lettuce species in North America.
Several species in this group have uncertain host affiliations. Aulacidea abdita was described by Alfred C. Kinsey in 1920 from adults dissected from old stems that he considered to be Canadian lettuce. Unfortunately, his specimens were greatly damaged (the stems were over 40 years old by the time he dissected them!), but several characters of the head and wings make this species distinct enough. I have not yet encountered this species amongst material my collaborators and I have reared, and I am rather doubtful that Canadian lettuce is the correct host plant for this species. Similarly, we have found galls resembling Aulacidea podagrae on Florida lettuce (Lactuca floridana), but the identity of the inducer remains unclear.
Overall, collecting material from more lettuce species is essential in understanding the biodiversity of these insects, and will help us better understand which plants are used by which wasps. At this time, it seems that only native lettuce species are galled by cynipid wasps.
Silphium Gall Wasps
This group is by far the most diverse group of Aulacideini in North America. Species associated with plants of the genus Silphium were originally found on just four Silphium species, but we’ve found many new species and many new host plants since the last major studies of the group. Species in the below table are grouped based on the location and type of gall they induce.
Species | Distribution | Host plant | Galled organ | Gall shape | Adults? | Sequenced? |
---|---|---|---|---|---|---|
Flower Gall Wasps (Antistrophus laciniatus species complex) | Apparently widespread in Eastern, Midwestern, and Southern US | Flowers | Kernel-shaped galls, solitary or clustered, often hidden in disc flower | |||
Antistrophus bicolor | Silphium integrifolium | Yes | Yes | |||
Antistrophus laciniatus | Silphium albiflorum, S. laciniatum, S. terebinthinaceum | Yes | Yes | |||
Antistrophus sp. nov. | Silphium perfoliatum | Yes | Yes | |||
Antistrophus sp. nov.? | Silphium gracile | Only a few old adults from museum collections | No | |||
Globular Stem Gall Wasps | Apparently widespread in Eastern, Midwestern, and Southern US | Stems | Large, round to clustered swellings | |||
Antistrophus silphii | Silphium asteriscus var. trifoliatum, S. compositum, S. gracile, S. integrifolium, S. perfoliatum, S. radula | Apical stems | Large round galls, often at tips of short stems | Yes | Yes | |
Antistrophus sp. nov. | Silphium integrifolium | Lower stems | Clustered galls, on middle or lower stems | Females only! | No | |
Antistrophus sp. nov. | Silphium perfoliatum | Lower stems | Clustered galls, on middle or lower stems | Males only! | No | |
Cryptic Gall Wasps | Apparently widespread in Eastern, Midwestern, and Southern US | Cryptic cells hidden within tissue | ||||
Antistrophus jeanae | Silphium perfoliatum | Stems | Yes | Yes | ||
Antistrophus meganae | Silphium terebinthinaceum; also hybrids of S. terebinthinaceum and S. laciniatum | Stems | Yes | Yes | ||
Antistrophus minor | Silphium laciniatum | Stems | Yes | Yes | ||
Antistrophus rufus | Silphium laciniatum | Stems | Yes | Yes | ||
Antistrophus sp. nov. | Silphium laciniatum, S. terebinthinaceum | Leaf veins and petioles | Yes | Yes | ||
Antistrophus sp. nov. | Silphium asteriscus var. trifoliatum | Stems | Yes | Yes | ||
Antistrophus sp. nov. | Silphium dentatum | Stems | Yes | Yes | ||
Antistrophus sp. nov. | Silphium integrifolium | Stems | Yes | Yes | ||
Leaf Blister Gall Wasps — unsure how many species, but all undescribed! | Apparently widespread in Eastern, Midwestern, and Southern US | Silphium gracile, integrifolium, radula | Leaf membrane along midrib | Large blisters in leaf tissue, most apparent on underside of leaf | No | No |
Comprising at least 14 species, Silphium gall wasps represent one of the most diverse gall wasp communities associated with a single plant genus, behind those on oaks and roses. Given the uncertain status of several species (especially those inducing leaf blister galls), further sampling of Silphium is essential within further understanding the diversity of these insects. Brock and Weakley’s 2020 treatment of Silphium recognizes 27 species and varieties, and thus far we’ve only sampled a handful for the presence of cynipid galls. The remaining ~20 Silphium taxa are almost certainly hosting a tremendous diversity of gall wasps, and there are almost certainly undiscovered gall morphotypes. Our sampling has focused on the Midwestern Silphium, but species in the Southeast and Southcentral United States are prime targets for further sampling.
Interestingly, the vast majority of Silphium gall wasps are specialists on a single host plant. Each species of Silphium gall wasp likely occurs throughout the range of its respective host plant(s), although it’s unclear whether all Silphium populations are capable of sustaining gall wasps. It seems that the wasps prefer large, native populations, although prairie restorations are also frequently found to contain galls.
Species | Distribution | Host plant | Galled organ | Gall shape | Adults? | Sequenced? |
---|---|---|---|---|---|---|
Aulacidea hieracii | Great Lakes area | Hieracium umbellatum and possibly other Hieracium | Stems | Fusiform to clavate | Yes (but more would be good!) | Yes (but more would be good!) |
Aulacidea pilosellae | Canada? | Pilosella spp. | Leaves | Blister | No | No |
Aulacidea subterminalis | US & Canada? | Pilosella spp. | Stolons | Elliptical to clustered | No | No |
Aulacidea sp. nov. | California (only one record so far) | Hieracium albiflorum | Leaves | Blister | No | Yes (from dissected larvae) |
Several species of herb gall wasps induce galls on true hawkweeds (Hieracium) and mouse-eared hawkweeds (Pilosella). Two of these species have been introduced as control agents for invasive plants, and it’s unclear whether the other species are native or represent introduced populations.
I recently found the first known galls of a species inducing leaf galls on Hieracium albiflorum in California! Thus far, I have been able to sequence the larvae of this gall wasp, but we have not yet been able to rear adult insects, which would be necessary to describe this species.
It’s quite likely that more species in this group exist, as we have not heavily sampled hawkweeds in North America. Searching prominent native species such as rattlesnakeweed (H. venosum) would be a great way to find potential new species.
Species | Distribution | Host plant | Galled organ | Gall shape | Adults? | Sequenced? |
---|---|---|---|---|---|---|
Aulacidea acroptilonica | Pacific Northwest | Rhaponticum repens (this species has been classified in many genera over time) | Stems | Fusiform to clustered | Yes | Yes |
Aulacidea sp. nov. | California | Unknown! | Unknown! | Unknown! | Yes (only old museum material) | No |
Aulacidea nabali | Widespread in Eastern and Midwestern US and Canada | Nabalus spp. | Lower stems, often below soil line | Elliptical to clustered | Yes (only old museum material) | No |
Antistrophus chrysothamni | Arizona | Chrysothamnus??? | Stems | Elliptical to clavate | Yes (only old museum material) | No |
Liposthenes glechomae | Widespread | Glechoma hederacea | Stems and leaves | Blister-like to elliptical | Yes | Yes |
These taxa are those that don’t fit neatly into another category and represent several different lineages. Several of these species are poorly characterized, known only from a small series of museum specimens, and one new species is known entirely from four female specimens collected in California.
In the case of Antistrophus chrysothamni, the species was first described in 1908, and it has been nearly a century since a valid record has been taken. The species was originally described as galling Chrysothamnus, but no galls matching those of this wasp have since been found on these plants. As a result, it is unclear what the true host plant is for this species, and acquiring new material would be essential in understanding the biology and classification of Antistrophus chrysothamni.
Collecting and Rearing Herb Gall Wasps
Collecting herb gall wasp galls is the most rewarding way to study these insects. Collecting and rearing a single gall will likely yield a great diversity of insects, including the offspring of the gall inducer as well as parasitoids and other gall inhabitants.
Many herb gall wasps induce what are called “cryptic” galls , meaning they induce galls that are not discernable based on external changes to the plant tissue. The widespread presence of cryptic galls has likely greatly contributed to our lack of knowledge about these insects due to the inherent challenges in locating and sampling them. Cryptic galls are best located by finding a large population of a potential host plant and dissecting a series of stems. Stems containing cryptic galls will likely display numerous oval-shaped chambers within the stem tissue as well as numerous larvae inhabiting the chambers. Once you’ve confirmed the presence of cryptic galls, you should collect entire stems of that plant. You can cut them into pieces to store and rear them (see remarks in the following paragraphs). In most cases, the base of the stem is the most densely populated part of the stem, so you should be sure to collect the entire above-ground part of the stem when sampling for cryptic galls.
The following excerpt from our Field Guide to Herb and Bramble Gall Wasps of North America provides an overview for collecting cynipid galls. If you have any questions about collecting or rearing these galls, please do not hesitate to contact me!
Key collection targets are organized into three groups: known species that require further sampling, a list of host plants that are likely to host gall wasps, and a list of plant genera that are more speculative in their possible role as gall wasp hosts. Use the following hyperlinks to navigate these lists:
List of Known Gall Wasps to Look For
List of Likely New Host Plants
List of Speculative Host Plant Genera
List of Known Gall Wasps to Look For
The species in this list are known species that require more study before description or re-description.
Genus and species | Host plant | Host organ galled | Distribution |
---|---|---|---|
Antistrophus spp. | Silphium spp. | Leaves (blister galls) | Widespread |
Antistrophus chrysothamni | Chrysothamnus? | Stems | Arizona |
Antistrophus laciniatus | Silphium albiflorum (I have sequence data for other known hosts already) | Flowers | Texas |
Antistrophus sp. nov.? | Microseris paludosa | Stems | California |
Antistrophus sp. nov.? | Uropappus lindleyi | Stems | California |
Aulacidea nabali | Nabalus spp. | Lower stems (often below soil) | Widespread in Eastern US and adjacent Canada |
Aulacidea sp. nov. | Hieracium albiflorum (possibly other species too) | Leaves (blister galls) | California; probably more widespread |
List of Likely New Host Plants
The plant species listed in this table belong to genera that host gall wasps, but gall wasps have yet to be found on these specific species. Given the host use trends of known species, it is quite likely that these plants host gall wasps (and probably species new to science) given that other species in their genera are hosts.
Family | Genus and species | Distribution | Possible galled plant parts |
---|---|---|---|
Asteraceae | Hieracium | Widespread in US and Canada | Stems, stolons, and leaves |
Hieracium abscissum | Southwestern US and Mexico | ||
Hieracium argutum | California | ||
Hieracium bolanderi | Southwestern US and Baja California (Mex.) | ||
Hieracium brevipilum | Southwestern US | ||
Hieracium carneum | Southwestern US and Chihuahua (Mex.) | ||
Hieracium crepidispermum | Southwestern US and Mexico | ||
Hieracium fendleri | Southern US and Mexico | ||
Hieracium greenei | Pacific Northwest | ||
Hieracium gronovii | Eastern North America | ||
Hieracium horridum | Pacific Northwest & Nevada | ||
Hieracium longiberbe | Pacific Northwest | ||
Hieracium longipilum | Central US and Canada | ||
Hieracium megacephalon | Southeastern US | ||
Hieracium nudicaule | Pacific Northwest | ||
Hieracium paniculatum | Eastern North America | ||
Hieracium parryi | Pacific Northwest | ||
Hieracium pringlei | Southwestern US | ||
Hieracium robinsonii | Far North (Maine, New Hampshire, and adjacent Canada) | ||
Hieracium scabrum | Eastern North America | ||
Hieracium schultzii | Texas and Mexico | ||
Hieracium scouleri | Northwestern North America | ||
Hieracium traillii | Appalachian and Mid-Atlantic US | ||
Hieracium triste | Western US | ||
Hieracium venosum | Eastern North America | ||
Hieracium vulgatum | Northern North America | ||
Asteraceae | Lactuca | Widespread in US and southern Canada | Only stem galls known (both cryptic and visible galls) but other organs may have undiscovered galls |
Lactuca floridana | Widespread | ||
Lactuca graminifolia | Southern US | ||
Lactuca hirsuta | Widespread | ||
Lactuca ludoviciana | Southern and Midwestern US | ||
Asteraceae | Lygodesmia | Widespread in Western US; also Florida and Georgia | Stems (both upper stems and basal stems below soil) |
Lygodesmia aphylla | Florida and Georgia | ||
Lygodesmia grandiflora | Western North America | ||
Lygodesmia ramosissima | Texas and Mexico | ||
Lygodesmia texana | Southcentral US and Mexico | ||
Asteraceae | Microseris | Western North America, mostly West Cost | Stems |
Microseris acuminata | West Coast | ||
Microseris bigelovii | West Coast | ||
Microseris borealis | West Coast up to Alaska | ||
Microseris campestris | California | ||
Microseris elegans | California | ||
Microseris howelii | Oregon | ||
Microseris laciniata | West Coast | ||
Microseris nutans | Widespread in Western US and Canada | ||
Microseris sylvatica | California | ||
Asteraceae | Pyrrhopappus | Widespread in Eastern and Central US | Stems |
Pyrrhopappus carolinianus | Eastern and Central US | ||
Pyrrhopappus pauciflorus | Texas and Mexico | ||
Pyrrhopappus rothrockii | Arizona, New Mexico, and Texas | ||
Asteraceae | Silphium | US and parts of southern Canada | Stems, flowers, leaves (both cryptic and visible galls) |
Silphium albiflorum | Texas | ||
Silphium asperrimum | Southcentral and Southeastern US | ||
Silphium asteriscus (and varieties) | Southeastern US | ||
Silphium brachiatum | Southeastern US | ||
Silphium compositum (and varieties) | Southeastern US | ||
Silphium confertifolium | Alabama | ||
Silphium connatum | Mid-Atlantic US (VA, WV, NC) | ||
Silphium dentatum | Southeastern US | ||
Silphium glutinosum | Bibb County, Alabama | ||
Silphium gracile | Southcentral US | ||
Silphium mohrii | Appalachian US | ||
Silphium perplexum | Alabama | ||
Silphium pinnatifidum | Appalachian and Southcentral US | ||
Silphium radula | Southcentral US | ||
Silphium reniforme | Southeastern US | ||
Silphium simpsonii | Southeastern US | ||
Silphium speciosum | Lower Midwestern US | ||
Silphium wasiotense | Appalachian US |
List of Speculative Host Plant Genera
The plant genera listed in this table might host gall wasps based on relatedness to taxa already known to host gall wasps. These taxa are much more speculative than those in the above table, but may prove to be hosts of notable gall wasp diversity.
Plant Genus | Distribution |
---|---|
Subtribe Crepidinae (2 genera listed here; this tribe includes Nabalus which has a known gall wasp) | Widespread in North America |
Crepis (Several native spp. worth checking) | Widespread in North America |
Taraxacum (Several native spp. worth checking) | Widespread in North America |
Subtribe Microseridinae (18 genera listed) | Primarily western North America |
Agoseris (11 spp.) | Western North America |
Agoseris (11 spp.) | Western North America |
Anisocoma (1 sp. – A. acaulis) | Southwestern US |
Atrichoseris (1 sp. – A. platyphylla) | Southwestern US and Northwestern Mexico |
Calycoseris (2 spp.) | Southwestern US and Northwestern Mexico |
Chaetadelpha (1 sp. – C. wheeleri) | Southwestern US |
Glyptopleura (2 spp.) | Southwestern US |
Krigia (7 spp.) | Eastern North America |
Malacothrix (18 spp.) | Western US and Northwestern Mexico |
Marshalljohnstonia (1 sp. – M. gypsophila) | Coahuila, Mexico |
Munzothamnus (1 sp. – M. blairii) | California |
Nothocalais (4 spp.) | Western and Central North America |
Pinaropappus (2 US spp.) | Southern US and most of Mexico |
Pleiacanthus (1 sp. – P. spinosus) | Western US |
Prenanthella (1 sp. – P. exigua) | Southwestern US |
Rafinesquia (2 spp.) | Southwestern US |
Shinnersoseris (1 sp. – S. rostrata) | Central North America |
Stephanomeria (14 spp.) | Western North America |
Comentarios
Tagging some of the folks I think might appreciate this more-detailed post:
@calconey @megachile @nancyasquith @arbonius @graysquirrel @friesen5000 @ceiseman @adeans
I love this, well done Louis!
This is great!
Wow, great work! I didn't know this function of iNat. Very useful.
Incredible work here!
Collecting/surveying some L floridana is on my agenda for my fall gall trip this year... supposedly we have L hirsuta here as well although there is really only one good modern herbarium record for the whole state.
I have never seen (noticed) the Silphium leaf blister galls here in Ohio, but I will run through a few sites this fall and see if I run into any.... looking like I wont be getting back into the south for some new Silphium species until next spring.
I have not really look at hawkweed with any seriousness, and they are somewhat common so will start to keep an eye out for them when I run into them. Looks like we have a handful of species here in OH
I have looked at quite a bit of Nabalus with no success so far, even at pretty dense sites... wondering about timing on this one, and going to keep track of how these die down so I can find them during the winter this year.
Crepis and Krigia is decently common here so that goes on the list as well...
@calconey The second-ever iNat observation of Aulacidea nabali was just posted from northeastern Canada so the galls should be developed at our latitude at this time. I'm planning a trip to find it this weekend at a nearby preserve with records of Nabalus - hopefully I find some! Cryptic galls are definitely worth searching for on these plants as well.
Thanks for keeping an eye out! I'm sure we'll come up with some interesting taxa this coming season.
I found this post while searching for a possible gall-inducer on Prenanthella exigua, which is among the "speculative host plant genera" listed above. Observation here: https://www.inaturalist.org/observations/213625057
In some areas, ~50% of the plants had this same gall. I can probably collect and try to rear some!
@lithostrotionella those could certainly be an undescribed gall wasp - the best way to tell what kind of insect induced them is to take a simple cross section. If you’d be willing to collect some of these, I could also sequence the DNA of the insects inside. Based on what I’ve seen, these could be a new genus and not just a new species. I’d be greatly interested in anything you’re able to find!
I was wondering if you have encountered galls on Heliantheae? I found this wasp yesterday on Helianthus tuberosus and had one last year as well: https://www.inaturalist.org/observations/237346576
Thanks
Bob Noble
Hi @bob15noble! The wasp in your photos is one of the parasitic Cynipoidea rather than one of the gall-making species. It was probably attacking an insect concealed in the flower or maybe just resting. Have you ever seen galls themselves on Helianthus? There are some midges know to make galls on true sunflowers but there are records from old museum specimens suggesting that gall wasps may also be associated with certain Helianthus
Thank @louisnastasi. I haven't seen them on sunflowers but will certainly keep an eye out for them.
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