Diplolepis gracilis

Diplolepis nebulosa

Diplolepis triforma

Diplolepis bicolor

Diplolepis rosaefolii

Diplolepis ignota

Diplolepis bassetti

Diplolepis variabilis

Diplolepis fusiformans

Diplolepis nodulosa

Diplolepis spinosa

Diplolepis radicum

Diplolepis polita

Diplolepis gracilis (Ashmead)

Diplolepis gracilis was first described from galls collected at an undisclosed site in the northeastern United States (Ashmead 1897). Little is known about the distribution of D. gracilis. However, it has been recorded from several northern states (Thompson 1915; Olson 1964; Burks 1979). On the prairies, galls are found on roses growing in shaded areas along the North Saskatchewan River in Edmonton, Alberta, eastward toward Prince Albert, Saskatchewan, and northward along the South Saskatchewan River from the Alberta– Saskatchewan border. 

Mature galls are ellipsoid, averaging 4–6 mm in diameter, have blunt protuberances extending from the lateral circumference, and are on the abaxial surface of leaflets (Fig. 26). They are single-chambered (Fig. 27) with thin walls. Maturing galls are white and although they are usually found in rows, adjacent galls seldom coalesce. Mature galls turn light tan and fall with their host leaves in mid-September. Galls are initiated in late summer. 

A large population of galls found near Douglas Provincial Park in Saskatchewan illustrates a typical community for this species (Fig. 44H), of which 12.7% were inducers and 21% were Periclistus. The most abundant parasitoids were Orthopelma (at 30.5%) and Aprostocetus (26.4%). Eurytoma were relatively low at 2.6%. Only about 20% of the immature galls sampled at another site in central Saskatchewan in mid-season had Periclistus and 19.1% by the time the galls matured (Table 5). The mean number of Periclistus per mature gall is also low (Table 4). No parasitoids mature and exit mature galls in the season of gall induction (Table 3).

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 triforma Shorthouse and Ritchie

Diplolepis triforma was first described from galls collected near Sudbury, Ontario (Shorthouse and Ritchie 1984). It was given this name because three types of galls can be induced by larvae from the same female. They are found on R. acicularis throughout the Aspen Parkland Ecoregion and R. woodsii on the prairies and in southern British Columbia. This species is found across southern Canada and the Yukon and is usually sparsely distributed. 

Immature galls are green swellings at the base of the apical meristem and usually are covered with dense spines. Galls are initiated in the early spring. Mature galls are conspicuous, woody, and firmly attached to twigs. Most galls are pear-shaped without distal stem growth (Fig. 38). However, about one-quarter of the galls have some distal growth and a few are fusiform swellings of a twig distal to its base. The gall is multi-chambered and the chambers are close to the surface (Fig. 39). They remain on their hosts over the winter. 

Wiebes-Rijks and Shorthouse (1992) provided data on the inhabitants associated with a large population of galls near Sudbury, Ontario, for which the most common parasitoids were Eurytoma spp, Pteromalus, Torymus sp., and Orthopelma sp. Periclistus are not associated with this gall.

Diplolepis bicolor (Harris)

Diplolepis bicolor was first described from galls collected at an unidentified locality in the northeastern United States (Harris 1841). It has a wider distribution in southern Canada than D. polita, being found from British Columbia to Nova Scotia but not in Newfoundland. Earlier workers have recorded the gall from Calgary (Weld 1926) to Alabama (Thompson 1915). 

Mature galls are spherical, averaging 7.0–11.0 mm in diameter. They usually occur in dense clusters averaging eight galls per cluster and are clothed with sharp, stiff spines (Fig. 18). Galls are induced on the adaxial surface of leaflets but usually grow in a dense mass firmly attached to the shoots. Galls often remain on the shoots over the winter. They occur on all three species of prairie roses but are most common on R. woodsii. 

Galls are single-chambered (Fig. 19) with walls much thicker than those of D. polita. Immature galls are either leaf green, yellow, or bright red. Most galls turn yellowish-brown as they mature, although some are bright red until they dry. Eggs are deposited in early May on the adaxial surface of immature leaflets (Shorthouse et al. 2005). Periclistus-modified galls are larger than inducer-inhabited galls. 

Because populations of D. bicolor galls are usually widely scattered, it is difficult to obtain sufficient numbers to assess the community. However, a large population of galls found about 25 km east of Saskatoon, Saskatchewan, provided this information. The galls were heavily attacked by Periclistus (Fig. 44B), which is always the most abundant inhabitant. About 59% of the immature galls were inhabited by Periclistus and about 28% of the mature galls by the end of the season (Table 5). Inquiline-modified galls contained an average of 9.3 chambers (Table 4). By fall, only 5.5% of the inhabitants were inducers (Fig. 44B), which is typical throughout the range of this species. Parasitoids constituted about 32% of the remaining inhabitants (Fig. 44B), the most common being Eurytoma sp. and Pteromalus sp. About 39% of the Eurytoma sp. exited in the current year (Table 3), as did some of the Torymus and Pteromalus.

Diplolepis rosaefolii (Cockerell)

Diplolepis rosaefolii was first described from galls collected in Colorado (Cockerell 1889). It has the widest distribution of all Nearctic Diplolepis, being found from British Columbia to Newfoundland and from the Yukon and Alaska to Colorado. It is a common species on the prairies and in southern British Columbia. 

Diplolepis rosaefolii is one of the smallest adults in the genus, along with D. fusiformans, averaging about 2 mm in length. Galls are lentil-shaped (Fig. 20), 2.0–2.5 mm thick, and 3.0–5.5 mm in diameter and protrude from both the adaxial and abaxial surface of leaflets. Galls usually occur scattered over the leaf, although sometimes they are densely packed and coalesced. They are usually the same colour as the host leaflet when immature but turn either pale yellow or bright red when mature. They are single-chambered with the larva lying parallel to the leaflet surface (Fig. 21). Immature galls appear from late spring to late summer, indicating the adults have a lengthy activity period. 

This species appears to be the least host specific of all Diplolepis in Canada, being found on the three prairie species of Rosa. Galls are most common on short, bushy R. woodsii growing in dry sites in the Mixed Grassland Ecoregion. Most galled leaves abscise in mid-fall, but heavily galled leaves sometimes remain on the plants over the winter. 

Galls of D. rosaefolii from coulees of the South Saskatchewan River near Langham, Saskatchewan (west of Saskatoon), illustrate the community typical for this species (Fig. 44C). Commonly, 50–75% of all inhabitants are inducers throughout the range of this species. Periclistus are also common, frequently accounting for 12–25% of all inhabitants. Eurytoma, Pteromalus, and Glyphomerus stigma are the most common parasitoids (Fig. 44C). The percentage of galls inhabited by Periclistus is high in mid-season but drops to less than 15% by the end of the season (Table 5). Fewer Periclistus larvae occur per gall than in the galls of other species (Table 4). About one-third of the Eurytoma exit galls in the year of induction, as do over half of the Pteromalus (Table 3).

Diplolepis ignota (Osten Sacken)

Diplolepis ignota was first described from galls collected at undisclosed locations in the eastern United States (Osten Sacken 1863). Beutenmüller (1907) and Kinsey (1920) provided descriptions of the adults. This species has been recorded in Minnesota (Olson 1964), the eastern United States (Beutenmüller 1907), and as far south as Florida (Thompson 1915). It is found in the Mixed Grassland Ecoregion across the driest regions of southern Alberta and Saskatchewan. 

Galls are found on the abaxial surface of leaflets and are variable in shape and size. Single galls are spherical, but they usually coalesce to form irregularly rounded, often reniform masses (Fig. 24). Two or three masses commonly form in one large elongated cluster that causes host leaves to droop. Galls are single-chambered (Fig. 25), but when they coalesce, they appear multi-chambered. Single-chambered galls when mature average 6–9 mm in diameter. Reniform galls average 15–20 mm in length. Mature galls become hard and woody when they dry but are soft and spongy when wet. They have a smooth surface without spines or protuberances. Galls are initiated in early August. Mature galls are light tan and remain attached to their hosts. 

Galls are found only on R. arkansana in Alberta and Saskatchewan, especially on those species growing sparsely on the flood plains in river valleys in areas without overgrowth or in open prairies without other shrubs. Beutenmüller (1907) and Kinsey (1920) reported galls on R. blanda, R. carolina, R. virginiana, and R. nitida in eastern North America. 

Three populations of D. ignota galls are included here for an overview of the component communities. One population (Fig. 44E) was found on the flood plain of the Oldman River north of Coaldale, Alberta. Rosa arkansana here were growing among patches of R. woodsii on which galls of D. nebulosa and D. bassetti were common. The second site was a pure stand of R. arkansana about 2 km away on the level prairie above the flood plain (Fig. 44F) and was chosen to compare two communities near one another. The third site was an isolated patch of R. arkansana growing on native shortgrass prairie about 20 km north of Maple Creek, Saskatchewan. This circular patch of roses was about 50 m in diameter and most plants were galled. Galls at all three sites were collected in the spring and returned to the laboratory to emerge the adults. 

Low numbers of inducers were present at the two Coaldale sites (Fig. 44E and F), but 23.5% of the inhabitants were inducers at the Maple Creek site (Fig. 44G). Few Periclistus were among the inhabitants at all three sites. Parasitoids constituted 75.8–92.5% of individuals recovered at each site. Aprostocetus was the most dominant parasitoid, followed by Eurytoma and Orthopelma. Communities at the two Oldman River sites were remarkably similar, whereas the Maple Creek site had more inducers. The reason for the differences could be that the Maple Creek site was more recently established and the parasitoids had yet to become established. 

From a typical population of galls east of Saskatoon, Saskatchewan, 11.4% of galls in mid-season were inhabited by Periclistus and 5.8% by the end of the season (Table 5). The mean number of Periclistus larvae per gall was 2.9 (Table 4), with only 1.9% of the Eurytoma exiting in the year of gall induction (Table 3). Similar data were not obtained from the sites used for the communities summarized in Fig. 44.

Diplolepis bassetti (Beutenmüller)

Diplolepis bassetti was first described from galls collected near Corvallis, Oregon (Beutenmüller 1918). However, the gall illustrated by Beutenmüller is that of the European multi-chambered gall of D. rosae, whereas galls of D. bassetti are single-chambered. Because D. rosae is established in Oregon, this early report likely confused the two species. Kinsey (1922) provided a detailed description of the adults and recognized two subspecies. However, he also appears to have confused the galls of D. bassetti and D. rosae. 

Diplolepis bassetti induces mossy, monothalamous galls (Figs. 28 and 29) on the adaxial surface of the leaflets of R. woodsii in open habitats in southern Alberta and Saskatchewan and in the Okanagan Valley of British Columbia. Diplolepis bassetti is also sparsely distributed across southern Alberta and southwestern Saskatchewan. 

Galls are usually found in dense clusters. Their surface is covered with soft filamentous hairs (Fig. 29) that are green to red when immature, turning brown when mature. Galls are initiated in mid-summer. The chambers rarely coalesce and the individual galls can be easily separated. Galls average 4–5 mm in diameter. They commonly remain attached to the host plant throughout the winter. 

Two large populations of mature galls collected in the spring were chosen to illustrate community composition. One collection was made on the flood plain of the Oldman River north of Coaldale at the same site as the D. ignota galls (Fig. 44E). The second was made from several large patches of roses from Kelowna to Osoyoos, British Columbia. No data were obtained on the seasonal changes of Periclistus attack, the number of Periclistus per modified gall, or the percentage of parasitoids exiting galls in the fall. 

Inducers were by far the most abundant inhabitants (Fig. 44I) at the southern Alberta site. Galls here also had few Periclistus, representing 2.8% of the community. Only 19.6% of the remaining inhabitants were parasitoids, with the most abundant being Pteromalus (7.8%) and G. stigma (7.5%). In contrast, galls from southern British Columbia (Fig. 44J) had fewer inducers (16%) and Periclistus were much more abundant (28.4%). Parasitoids constituted 55.3% of the emergents, with the most abundant being Aprostocetus (46.9%) and Eurytoma (5.5%).

Diplolepis variabilis (Bassett)

Diplolepis variabilis was first described from galls collected in North Dakota (Bassett 1890). Beutenmüller (1907) and Kinsey (1922) reported galls from Washington to Texas. In Canada, D. variabilis is found only west of the Rocky Mountains and is very common on tall R. woodsii from Kelowna to Osoyoos, British Columbia. Galls of D. variabilis are found on the leaves of the upper branches and are usually larger and denser than galls of D. ignota. 

Galls are single-chambered and spherical and are found on the abaxial surface of leaflets. However, most galls coalesce to make clusters irregularly rounded and globular to ovate (Fig. 30). Single-chambered galls are about 8 mm in diameter, whereas coalesced galls are often 2 cm in diameter. They have a smooth surface and internally are pith-like with the consistency of packed sawdust. The chambers are located at the centre, deep within the galls (Fig. 31). Galls are green when immature but turn tan to brown when mature. They are often so dense that branches droop with the combined weight of the galls. They remain on the host plants over winter. Galls are initiated in late summer. 

Inhabitants were reared from a large population of galls collected in the fall near Oliver, British Columbia. Of recovered insects (Fig. 44K), 7.7% were inducers, 23.2% were Periclistus, and 69.3% were parasitoids. The most abundant parasitoids were Aprostocetus at 47.5% and Eurytoma at 17%.

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 nodulosa (Beutenmüller)

Diplolepis nodulosa was first described from galls collected in the northeastern United States (Beutenmüller 1909). A detailed description of adults was provided by Brooks and Shorthouse (1997). Galls of D. nodulosa are tiny swellings at the tips of stems of R. woodsii and are barely perceptible (Fig. 34). 

Mature galls are single-chambered, fusiform, and spineless (Fig. 34). They average 3.1 mm in diameter and are commonly circumscribed by a series of stunted leaflets. Galls are green when immature but frequently turn red when mature. Larvae are usually found in a vertical position within their chambers (Fig. 35). 

Periclistus greatly enlarge inhabited galls (Fig. 36), making them highly visible and indicating that D. nodulosa is in the area. Galls modified by Periclistus (Figs. 36 and 37) are multi-chambered, spherical structures averaging 12 cm in diameter, with some galls being 20 mm in diameter. Galls found near Sudbury, Ontario, contained an average of 17 Periclistus per gall (maximum of 146) (Brooks and Shorthouse 1997) and prairie galls are likely similar. Immature Periclistus-modified galls are initially green but turn mottled red- brown in the fall and are gray-tan by the following spring. 

A closely related species, D. inconspicuous Dailey and Campbell, has been found in California on R. californica (Dailey and Campbell 1973). Its galls are identical to those of D. nodulosa, but the adults are morphologically distinct (Brooks and Shorthouse 1997). Diplolepis inconspicuous is apparently restricted to the west coast of the United States, whereas D. nodulosa is found throughout eastern and midwestern North America (Shorthouse and Ritchie 1984), east to the north shore of Prince Edward Island, and west to British Columbia. It is found on R. blanda in Ontario, R. virginiana on Prince Edward Island, and R. woodsii in British Columbia, Alberta, and Saskatchewan. 

For a large population of galls near Sudbury, Ontario, Periclistus killed 65% of the inducers and parasitoids killed an additional 17%. Communities of prairie galls are likely similar (Brooks and Shorthouse 1997).

Diplolepis spinosa (Ashmead)

The first report of Diplolepis spinosa was in Florida (Ashmead 1897), where the species was named from the characteristics of the gall. Gillette (1890) provided the first description of D. spinosa females but under the name Rhodites multispinosus. Burks (1979) recognized R. multispinosus as a synonym of D. spinosa. Beutenmüller (1907) and Kinsey and Ayres (1922) provided a more detailed description (as D. multispinosus) and illustrated the galls, as did Shorthouse (1988, 1993). 

Galls of D. spinosa are one of the most conspicuous galls on the grasslands. They are spherical or irregularly rounded and often the size of a golf ball (Fig. 40). They appear attached to the main stem but are formed from a leaf bud (Figs. 9–12). They are firmly attached to their hosts and often can be removed only with snips. 

Galls of D. spinosa are found from eastern Ontario to the Okanagan Valley and northeastern British Columbia. They are found only on R. woodsii on the prairies and in British Columbia and only on R. blanda in Ontario. They are never found on R. acicularis. Galls are usually weakly spined to smooth on the spiny R. woodsii on the prairies but always heavily spined on the smooth-stemmed R. blanda in Ontario. They average about 23 mm in diameter in Ontario (Bagatto and Shorthouse 1994) and those on the prairies are similar. 

Galls are multi-chambered (Fig. 41), with most chambers located in a cluster near the centre. Immature galls are yellowish-green, soft, and usually clothed with slender spines. Mature galls are reddish-brown or dull purple, hard, and woody. Galls on wild roses from central Ontario have an average of 16.5 larval chambers per gall (Bagatto and Shorthouse 1994). Those on the prairies and in British Columbia are likely the same.

Galls collected in the spring from southern Saskatchewan in the Great Sand Hills are used here to illustrate a typical component community. Commonly, 20–30% of the inhabitants associated with populations of this gall are inducers (Fig. 46L). Periclistus sp. make up about 21.3% of all inhabitants, whereas parasitoids form about 50% of all inhabitants. The most abundant parasitoid was Eurytoma sp. at 47.1% of all inhabitants.

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 polita

Diplolepis polita was first described from galls collected in the United States by Ashmead (1890). This species is now known to occur from the coast of British Columbia north to central Alaska and the Yukon, east to western Quebec, and from central Ontario north to James Bay. It is common throughout the Aspen Parkland Ecoregion from Alberta to Manitoba on roses in partially shaded areas at the edge of forests (Fig. 4). 

Mature galls are spherical, averaging 3.5–4.5 mm in diameter, clothed with weak spines, and found on the adaxial (upper) surface of leaves (Fig. 16). They are single-chambered (Fig. 17) with thin walls and usually grow in clusters, several galls per leaflet. Galls are found both on the sucker shoot and on multi-year roses. Galls always abscise in late summer. Immature galls in shaded areas are usually greenish-yellow, whereas those growing in areas open to the sun are often bright red. All turn light brown when dry. 

Galls of D. polita are found only on R. acicularis east of the Rockies, never on R. woodsii growing in open areas of the southern prairies. However, they are found on R. woodsii in more shaded areas in the Okanagan in British Columbia. A large population was found on R. arkansana near the top of the Cypress Hills in Alberta (Shorthouse 1991). 

A large population of galls from within Prince Albert National Park in Saskatchewan illustrates the composition of a typical component community (Fig. 44A). Only 4% of the inhabitants were inducers by fall, 29% were Periclistus, and the rest (67%) were parasitoids. Periclistus (average of 5.4 per gall; Table 4) were commonly found in about 70% of all maturing galls and 12% of mature galls (Table 5). The most common parasitoids were Eurytoma sp. and Pteromalus sp. (Fig. 44A). About half of the Eurytoma sp. and half of the Torymus sp. matured and exited galls by the end of the season (Table 3).

Galls induced by cynipid wasps of the genus Diplolepis (Hymenoptera: Cynipidae) on the roses of Canada's grasslands