Diplolepis radicum (Osten Sacken)

Diplolepis radicum was described from galls in the central United States (Osten Sacken 1863). Adult females are among the largest of the genus, averaging 3.0–4.0 mm in length. Kinsey (1922) and Shorthouse (1988) provided additional information on the adults.

Galls of D. radicum are by far the largest of all Diplolepis galls, ranging in size from 2.5 to 6.0 cm, with some 10 cm in diameter. They are found throughout the grasslands of the prairies and in southern British Columbia. However, they are difficult to locate, especially when partially buried in the ground or hidden by vegetation. They are formed at the tips of adventitious shoots (Fig. 1) just below the surface of the ground. Although galls of this species are commonly referred to as root galls because of their location, they are stem galls (Fig. 42).

Females crawl down cracks in the ground at the base of roses in early spring to locate adventitious shoots before they protrude above the surface. Large numbers of eggs, sometimes numbering 200–350, are laid within the shoot tips and the resulting larvae produce irregularly rounded, tomato-shaped, multi-chambered galls (Fig. 43) of variable size. Galls are soft and succulent when growing, with the larval chambers packed throughout the mass of the gall (Fig. 43). They always have a smooth surface and are reddish-brown throughout all stages of development.

Diplolepis radicum appears to be as widely distributed as D. spinosa. Diplolepis radicum has been recorded from Ontario to North Carolina on R. carolina and west to Colorado and north to Oregon and Washington State on R. nutkana and R. woodsii (Beutenmüller 1907, 1914; Weld 1926). Galls are found on R. woodsii across the prairies and appear to be most abundant where the soils are sandy. Galls are found on R. woodsii in southern British Columbia.

Less is known about the community of inhabitants associated with this gall than about those of other species. For inhabitants of 40 galls collected in the fall from the Great Sand Hills of Saskatchewan, 27.2% were inducers, 2.9% were Periclistus sp., and the rest were parasitoids. Eurytoma sp. and Pteromalus sp. were the most abundant parasitoids.

Diplolepis radicum (Osten Sacken, 1863)

Nomenclature: Rhodites radicum Osten Sacken, 1863 | Tribalia batatorum Walsh, 1864 | Rhoditesatahensis Bassett, 1890 | Diplolepis radicum var. johnsoni Kinsey, 1922 | Diplolepisradicum var. plana Kinsey, 1922 | Diplolepis radicum var. divergens Kinsey, 1922 |Diplolepis radicum var. angustior Hunter, 1923

Feeds on: Produces galls on Rosa carolina L., R. nutkana C. Presl, and R. woodsiiLindl.

Distribution: United States: Colorado, Connecticut, District of Columbia, Illinois,Indiana, Massachusetts, Minnesota, North Carolina, New Jersey, New York, Ohio,Oregon, Pennsylvania, Washington; Canada: British Columbia, Manitoba, Ontario

Diplolepis radicum

Large dark red galls at base of Rosa carolina usually hidden by debris

[Photo caption]

332. On Rosa carolina. Adults emerged June 10 (NY); June 2-16 (VA).

Diplolepis radicum

Although present in most regions, its galls are frequently overlooked because they form below the surface of the ground on the tips of shoots arising from rhizomes (Shorthouse 1988). Galls are variable in size and shape, but most are irregularly rounded and potato-shaped with numerous bulges (Fig. 7). The surface is smooth and tan to reddish brown throughout all stages of development.

Diplolepis radicum

GALL. — A large, massive, pithy root gall. Polythalamous, larger galls with a hundred or more larval cells. Very irregular in shape, but generally rounded, globular, depressed at the points of attachment, irregularly folded, gnarled, sometimes as an unopened bud; variable in size, up to 105. mm. in length by 70. mm. in diameter; reddish brown, darkening with age. Internally soft, rather pithy, with only a small amount of woody fiber; the larval cells large, nearly round, often 4. mm. in diameter, with a smooth but hardly distinct, inseparable lining. On stems and roots, under ground, or under debris close to the ground; sessile or nearly so, laterally or terminally, on roses.

RANGE. — Canada and Maine to North Carolina and Washington, Probably everywhere in North America where roses occur. The insects emerge rather late in the spring, in April or May or later, depending on the development of the season. Immature galls may be found in July or August. The species is bisexual, with the sexes about equal in numbers, and probably takes only a single year to mature, without an alternation of generations. The number of parasites bred is not great, altho they do occur. W. M. Davis (1908) records finding galls broken into by mice.

Diplolepis radicum variety radicum (Osten Sacken)

GALL. — Does not differ particularly from the galls of other varieties; averaging smaller.

RANGE.— D.C.: Washington (Osten Sacken). North Carolina (Beutenmuller) . Pennsylvania? (Beutenmuller) . New Jersey: Ft. Lee (Beutenmuller) . New York: Staten Island (Beutenmuller); Nyack (Zabriskie in Amer. Mus.).

Diplolepis radicum variety johnsoni, new variety

GALL. — Does not differ particularly from the galls of other varieties, averaging smaller.

RANGE. — Massachusetts : Gloucester. Not improbably occurs thruout more northern New England.

Probably no two localities in the United States have been more thoroly collected for Cynipidae than eastern Massachusetts and the neighborhood of New York City. It is no credit to the taxonomy we have been doing to have ignored the evident differences between material from the two regions. No two adjacent varieties of this species are more distinct than radicum and johnsoni. I have not yet worked out the extent of the cynipid fauna of eastern Massachusetts; it is probably the same as the fauna of most of more northern New England; variety radicum is very probably confined to the remnants of the old Atlantic Coastal Plain.

[Kinsey goes on to describe three more varieties, one of which is listed separately as Diplolepis utahensis]