Antistrophus lygodesmiaepisum Walsh, 1869

Nomenclature: Antistrophus pisum Ashmead, 1885 | Ascepiadiphila stephanotidis Ashmead, 1897

Feeds on: Induces galls on Lygodesmia juncea D. Don ex Hook

Distribution: United States: Colorado, Iowa, Kansas, Nebraska, Texas; Canada: Alberta, Saskatchewan

Antistrophus pisum

Pea-shaped galls scattered along stems of Lygodesmia juncea in autumn in ND, SD, KS, NE, WY, MO, CO.

[Photo caption]

349. On Lygodesmia juncea. Adults emerged from galls from North Dakota on Apr 10.

Asclepiadiphila stephanotidis, sp. n.

Host: Stephanotis sp. [mistaken?]

Gall: A small, rounded or pea-like gall averaging from 6 to 8 mm. in diameter, growing from the stems of a species of Stephanotis. Externally it is opaque and varies from a gray to a brownish colour, while internally it is whitish and composed of a dense pithy substance with a single larval cell in the centre.

Range: MO

Antistrophus pisum
Skeletonplant pea gall wasp

Host: Rush skeletonplant (Lygodesmia juncea).

Gall location: On the branches, often in large numbers on the same plant.

Description: These galls are small, ranging greatly in size from roughly 0.3-1.5 centimeters in diameter, and distinctly pea-shaped. Fresh galls are green and fleshy, and older galls are brown, dry, and rough. The galls develop on the outside of the branch rather than being directly integrated into the branch tissue.

Range: The established range for this species includes much of the Central United States and adjacent areas of Canada, from Manitoba south to Texas and west to Alberta.

The skeletonplant pea gall wasp is likely even more widespread within the range of its host plant, which is known from British Columbia south to southern California and east to Minnesota and Texas. This species has often been referred to as Antistrophus lygodesmiaepisum, but Antistrophus pisum is the most correct scientific name for the skeletonplant pea gall wasp. Specimens of this species have been mistakenly reported from several other host plants, including baccharis (Baccharis spp.) and wirelettuce (Stephanomeria spp.), but galls of this species only occur on rush skeletonplant.

Lygodesmiae pisum, new species

There is a rush-like plant about a foot high, with slender sprangling stems and a few rigid lance-shaped leaves, which inhabits Nebraska and the regions to the east and north of that territory, and is known to botanists as Lygodesmia juncea. On the stems of this plant there often grows a profusion of round or oval pea- like galls, ranging in diameter from 1/4 to 1/2 an inch, such as are represented in the annexed Figure 47. In the autumn each of these galls contains, in a central cavity about one-tenth of an inch in diameter, a fat yellow legless maggot, with a large round head and robust jaws tipped with black. Except the central cell, the rest of the gall consists of a dense whitish spongy matter, which ultimately becomes so hard as to be penetrated with some difticulty by the thumb-nail. About the middle of the following May there eats its way out of the gall, through a small pin-hole (Fig. 47, a), a black Gall-fly about one-eighth of an inch long, which scarcely differs in general appearance from the Oak-plum Gall fly (Vol. I. p. 104, Fig. 81) except in being so much smaller and in lacking the dark shade on the front wings. This Gall-fly is entirely new to science, and, as we have already explained, it is especially interesting because — growing as it does on a group of plants not hitherto known to be infested by Gall-flies — it presents structural characters different from those found in any other Gall-fly. In other words, a new genus has to be established to receive it, besides giving the characters separating it from any other species belonging to the same genus, which may hereafter be discovered. But as such details as these are only of interest to the scientific reader, we shall throw them into the form of an Appendix — to be "skipped " at discretion by the general reader.

Antistrophus pisum

Lygodesmia juneea Pursh (Skeleton weed). (Figure 5, a-h.) As shown in Fig. 5, three different galls were produced on Lygodesmia juneea Pursh by the gall maker, Antistrophus pisum Walsh. The typical gall is pea-shaped; another is a root gall; the third is a stem gall.

Figure 5. Galls on Lygodesmia juneea (Pursh) from which Antistrophus pisum Walsh emerged: a) Normal condition. b) Extreme crowding of galls. c) Root gall. d) to g) Fusiform galls. h) Normal galls with emergence holes through stems.

Antistrophus pisum Ashmead

Antistrophus pisum Ashmead 1885:294
Antistrophus ligodesmia-pisum Walsh 1869:74 (invalid name).
Asclepiadiphila stephanotidis Ashmead 1897b:263