Diplolepis fusiformans (Ashmead)

Diplolepis fusiformans was first described from galls found in Colorado (Ashmead 1890). They have also been found in Ontario, Illinois, Nebraska, and Arizona (Beutenmüller 1907; Kinsey 1922; Burks 1979; Caouette and Price 1989). Diplolepis fusiformans is one of the smallest wasps in the genus, with females averaging 1.5–2.5 mm in length.

Galls of D. fusiformans are small, fusiform, and found along the terminal parts of the current-year stems (Fig. 32) of R. woodsii. Galls may be a gentle swelling or may be swollen to about twice the size of the host stem (Fig. 32). Galled stems are smooth and often have a split in the epidermis. The gall is multi-chambered with a series of chambers, usually about five in a row, along the length of the stems (Fig. 33). Galls are internally woody, soft, and porous and the chambers are inseparable. Chambers containing Periclistus are also found along the lengths of the stem (Fig. 33).

Adults of D. fusiformans exit their galls in late June and oviposit in new sucker shoots about 5 cm in length. In contrast to all other species of Diplolepis, D. fusiformans deposits its eggs on the exposed surface of the stems (Shorthouse et al. 2005). The galls form after the larvae enter the stem.

Galls are found throughout the grasslands of the prairie provinces and southern British Columbia on R. woodsii. They have not been reported on R. arkansana or R. acicularis. In Ontario, D. fusiformans forms galls on R. blanda but not on R. acicularis. No data on the component communities associated with this gall were obtained.

Diplolepis fusiformans subsp. fusiformans (Ashmead, 1890)

Nomenclature: Rhodites fusiformans Ashmead, 1890

Feeds on: Induces galls on Rosa arkansana Porter, R. woodsii Lindl., and R. blanda Aiton

Distribution: United States: Arizona, Colorado, Illinois, Minnesota, Nebraska; Canada:British Columba, Ontario

Diplolepis fusiformans subsp. mendocinensis Kinsey, 1922

Nomenclature: Diplolepis fusiformans var. mendocinensis Kinsey, 1922

Feeds on: Induces galls on Rosa L. sp.

Distribution: United States: California

Diplolepis fusiformans subsp. minuta Kinsey, 1922

Nomenclature: Diplolepis fusiformans var. minuta Kinsey, 1922

Feeds on: Induces galls on Rosa L. sp.

Distribution: United States: California

Diplolepis fusiformans var mendocinensis

Rosa sp.
Stem swellings
Fusiform, 5 by 30 mm. Polythalamous. Type from Ukiah CA

Diplolepis fusiformans var minuta

Rosa sp.
Stem swellings
Fusiform, 3.5 by 20 mm, little swelling with not over 4 cells. From San Bernardino Mts CA.

Diplolepis fusiformans

Stem swellings
Smaller fusiform or abrupt one-sided corky enlargements of the stem, up to 30 by 7 mm.

[Photo caption]

335. On a wild rose. Adults emerged May 13-23; May 30-June 17 (Chi). Brodie reared the maker from galls on Rosa blanda June 18-20 and June 24-July 7 (Toronto).

Diplolepis fusiformans (Ashm.).

Rosa sp.
Puffy stem swellings on branches, 4–12 mm. long by 3 mm. in dia. , fissured, spongy inside, single or confluent. West Cliff, Colorado.

Diplolepis fusiformans

GALL. — Small, elongate stem swelling. Polythalamous, with rather few cells. Irregular, usually longer than wide, sometimes rather globose, more or less abrupt, usually but not always symmetrical about the stem, covered with brown bark somewhat different from the normal bark; up to 30. mm. long by 8. mm. in diameter, usually smaller, sometimes several more or less fused. Internally woody, rather solid, the normal stem tissue more evident centrally; the larval cells more or less elongate oval, the lining rather distinct but inseparable. On stems of Rosa species.

RANGE.— Canada: Toronto (Cosens). Illinois (Weld). Colorado. California. Probably occurs thruout North America, wherever roses occur.

This is one of the primitive species of the genus, as indicated by the closed radial cell, the small second abdominal segment, the equal numbers of the two sexes, and the slight development of the gall. It is not the same species as Diplolepis verna (Osten Sacken), altho both species are primitive. This species should be discovered wherever roses occur in North America, and many other varieties will need to be described. Of 236 insects I have bred, only 89, or 38 per cent, are males. But material of one variety gave over 50 per cent males, suggesting that the sexes are probably equal if the collections are adequate. The insects emerge in spring, from February further south to April (or later?) further north. It is unlikely that an alternation of generations occurs.

[Kinsey goes on to describe several varieties of this species which vary in gall morphology and range; see paper for details]