Diplolepis nebulosa

Diplolepis nebulosa was first described from unknown localities in the northeastern United States (Bassett 1890). Beutenmüller (1907, 1914) recorded the species from Connecticut, New York City, and Ontario. It is found sporadically across the prairies but sometimes occurs in such large numbers that hundreds can be collected in an hour. Galls are most commonly found on roses growing in the Mixed Grassland Ecoregion of southern Alberta and Saskatchewan.

Galls are spherical, averaging 5.0–7.0 mm in diameter, spineless, and on the abaxial leaf surface (Fig. 22). They occur singly or in a row and sometimes coalesce. Galls are green when immature and light brown when mature. They are single-chambered (Fig. 23) and the walls of mature galls are thin and brittle. Mature galls often abscise before their host leaves do. Periclistus-modified galls are larger and much firmer than inducer-inhabited galls. Galls are initiated in mid-spring.

Beutenmüller (1907) recorded galls on R. blanda and R. carolina L. in eastern North America. On the prairies and in southern British Columbia, these galls are found on R. woodsii. The most common habitat for D. nebulosa is on short R. woodsii, averaging 0.75 m in height and growing on dry, exposed sites. A large population of galls from the flood plain of the Oldman River northwest of Coaldale, Alberta, illustrates a typical community for this species (Fig. 44D). Inducers made up 8.8% of the inhabitants, whereas 32.1% were Periclistus. Parasitoids, mainly Orthopelma and Aprostocetus, formed 59.1% of the inhabitants. A higher percentage (66.6%) of galls were inhabited by Periclistus (average of 3.3 per gall; Table 4) in mid-season, which declined to 13.1% by the time galls were mature (Table 5). For Eurytoma and Torymus, 16.6% and 26.4%, respectively, of individuals exited galls by the fall (Table 3).

Diplolepis nebulosa (Bassett, 1890)

Nomenclature: Rhodites nebulosa Bassett, 1890

Feeds on: Induces galls on Rosa blanda Aiton and R. rubiginosa L.

Distribution: United States: Connecticut, New York; Canada: Ontario

Diplolepis nebulosa

Leaf galls
Similar [to D bicolor] but smaller, 5-6 mm in dia, the spines weak, on under side of leaf.

[Photo caption]

339. On a wild rose. Determination is questioned for the description says galls are 5-6 mm in dia and close to midrib on the under side of the leaf. Galls of this sort on rose in summer need further study.

Rhodites nebulosus n.sp.

Round, hollow, thin shelled, monothalamous galls three-sixteenths of an inch, or less, in diameter, on the underside of the leaves of the wild rose (Rosa blanda and probably R. carolina). They are usually situated on the lateral veins on the lower half of the leaf and close to the mid-vein. The surface in the green galls is quite smooth, but when dry it is slightly rough and uneven, but not pubescent. There is no larval cell.

These galls are often parasitized, and such are sometimes quite solid and contain several larval chambers. The same often occurs in galls of R. bicolor. I have received this species from correspondents in widely separated sections, but in most cases the galls were immature when collected and produced nothing, and 1 have only
one gall-fly, a male, of this species.

Diplolepis nebulosa

Mature galls are spherical, averaging 5.0–7.0 mm in diameter, spineless and on the abaxial leaf surface. They occur singly or in rows. They are most common on short R woodsii on dry exposed prairie. Immature galls are green to light brown with scaly, thick walls and a prominent depression distal to the point of attachment. Mature galls are pale brown and the depression is less prominent. Walls are thin and easily crushed between fingers. Larvae feed over the entire chamber surface. Adults removed from cold storage take an average of 26.3 days to emerge and are present in the field from mid-May to mid-June. Immature galls are found from early July to mid-August. Both immature and maturing galls appear together suggesting a lengthy period of gall initiation. Periclistus are found in 66.6% of the galls by mid-season and are major source of inducer mortality.