Antistrophus laciniatus species group
Rosinweed flower gall wasps

Hosts: White rosinweed (Silphium albiflorum), slender rosinweed (S. gracile), prairie rosinweed (S. integrifolium), compass plant (S. laciniatum), cup plant (S. perfoliatum), and prairie dock (S. terebinthinaceum). Galls will probably be discovered on additional rosinweed species as well.

Gall location: In the disk flowers, often concealed by the outer parts of the flower.

Description: Oval-shaped, kernel-like, single-chambered galls, typically clustered at the base of the disk flowers. Galls are often hidden, but carefully teasing away the outer flower layers will reveal the galls at the center. In some host plants, the flower is disfigured by the presence of galls (see photo below).

Range: This species group has been found throughout the Midwestern, Eastern, and South Central United States. Like many other herb galls, this group probably occurs throughout the entire ranges of each species’ respective host.

Historically, it was believed that all flower galls found on rosinweeds were induced by a single species, Antistrophus laciniatus; this species was described by Clarence Gillette in 1891. However, molecular evidence, along with careful morphological observations, suggests that there are several distinct flower gall wasp species on rosinweeds, each of which uses only a subset of the host plants from which flower galls are known. The identities of several of these putative species are still being examined; for instance, it is still unclear whether flower gall wasps on prairie rosinweed (Silphium integrifolium) and cup plant (S. perfoliatum) are induced by one species of gall wasp, or two separate species, each restricted to one host plant.

An additional species, Antistrophus bicolor, may be a rosinweed flower gall wasp, as it closely resembles other species in this complex. However, this species is known only from a single female collected in the late 1800s, and its host plant is not known. Hopefully, further collecting and rearing of disc flower galls on rosinweed will allow a verifiable association of this species and its true host plant.

Antistrophus laciniatus Gillette, 1891

Feeds on: Induces galls on Silphium laciniatum L.

Distribution: United States: Illinois, Kansas, Wisconsin

Antistrophus laciniatus

Silphium laciniatum
Galls hidden among the disk florets in flower head and found only when the head is broken open.

[Photo caption]

348. On Silphium laciniatum. Adults emerged the next spring.

Antistrophus laciniatus n. sp.

Galls.—Individual galls are egg-shaped, from 4 to 5 mm. in length, and occur in clusters un the receptacles of the flowers of Silphium laciniatum. (Plate IX., Fig. 8.) Mr. C. A. Hart has collected a number of these gall-clusters and in his description of them says : '' They always occur in well-ripened, healthy-looking flower heads, but do not show until the weather has removed the uninfested flowerets. They are always produced in the sterile flowers of the disk, towards the center."

Antistrophus laciniatus

Hosts: Silphium laciniatum, gracile, integrifolium

Range: KS, IL, WI, TX

[Texas record on S gracile is from a museum specimen without associated gall]

Gillette described this species as forming individual small (4-5mm), egg-shaped galls occurring in clusters in the flower disks of compassplant. Each gall supports on wasp. The galls occupy the center of the flower disk among the male (sterile) florets. The flowers appear unaffected by the wasps, with the fall slcuster becoming evident only as the flower head ripens and falls apart, revealing the galls.

Reported A laciniatus from four sites in Wisconsin.

Aylax laciniatus (Gillette)

Antistrophus laciniatus
Aulax laciniatus

Gall. (Plate XIV, Fig. 6.) In clusters on the receptacles of the flowers of rosinweed (Silphium laciniatum). Individual galls are egg-shaped and from 4 to 5 mm. in length.

Habitat. Illinois (Champaign).

According to Mr. C. A. Hart the galls occur in well-ripened, healthy looking flower heads, but do not show until the weather has removed the uninfested flowerlets. They are always produced in the sterile flowers of the disk, toward the center.