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 ignota (Osten Sacken, 1863)

Nomenclature: Rhodites ignota Osten Sacken, 1863 | Rhodites carolina Ashmead, 1887

Feeds on: Induces galls on Rosa arkansana Porter, R. blanda Aiton, R. carolina L., and R. nitida Willd.

Distribution: United States: Colorado, Connecticut, District of Columbia, Iowa, Illinois,Indiana, Massachusetts, Montana, North Carolina, New Jersey, New York,Pennsylvania, Washington; Canada: Manitoba, Saskatchewan

Diplolepis ignota

Leaf galls
Mealy Rose Gall. Globular, up to 15 mm in dia, several often coalescing itno a mass, covered with a mealy white bloom, hard, many-celled, attached on under side of leaf.

[Photo caption]

341. On a wild rose. Adults began to emerge Apr 15 (Chi); May 14-25 (NY)

Rhodites ignotus

Rhodites ignota
Rhodites carolina
Rhodites carolinus

Galls. — Irregularly globose leaf-galls (Figs. 5 to 7), covered with a white, mealy powder. Each gall is about globose, monothalamous, but often several galls coalesce to form large, elongate, more or less entire masses sometimes 20 mm. long. On the terminal twigs, petioles, and stems of the leaflets of Rosa blanda, R. Carolina , R. humilis, R. nitida , R. virginiana, and most likely other roses.

Range: Ontario, MA, RI, CT, NY, NJ, PA, MD, DC, NC, FL, IO, CO

The galls of Rhodites ignotus are first noticeable about the middle of August, somewhat deforming the leaves of the roses on which they are formed. The galls overwinter, sometimes on the bush, but often on the ground, to which they readily fall when the leaves bearing them wither in the autumn. The mature wasps are known to emerge the following spring from May to August, most of the adults appearing about the last of May or the first of June. As with R. rosae, this extended period of emergence is an unusual thing to find among the gall-wasps. Of thirty-seven of the wasps which I have bred, thirteen, i. e.. 35% of them were males, which is a higher percentage than that known from other species of the genus. However, incomplete observations on other breedings I have made would indicate a much lower percentage of males to be more nearly normal. The number of parasites obtained from these galls is extremely high : I have found them to constitute about 90% of all the insects bred — another instance of the ineffacacy of highly developed “protective” devices. Most of these parasites, are figitids, Synerginaj, etc , the so-called “inquilines,” but many other parasitic Hymenoptera also attack the galls.

The adults of ignotus live for only a few days at the most, oviposition often occurring only a few hours after emergence. The females will refuse to oviposit unless they find a bush in the right condition for receiving the eggs. A lot of the insects which I placed on a cultivated rose which was somewhat retarded in development refused to climb over the bush at all to examine the buds, though the same insects became active enough when placed on a plant in a more advanced state of development. They carefully examined the young leaves, hardly yet out of the buds, and in these leaves the eggs were laid. The quantities of parasites which emerged, mostly a couple of weeks after the cynipids, were very active in examining the leaves of the same plant and many of them were observed to oviposit, but whether into the eggs and very young galls of the gall-wasps I am not certain.

The points at which oviposition was made by the ignotus females were carefully marked and kept covered by gauze bags for almost a month and a half. The galls produced were first seen about the first of September, i. e., over a month and a half after the eggs were laid, but the degree of development of the galls indicated that they had appeared possibly two weeks earlier. The galls thus obtained were typical ignotus galls, in every way resembling the galls of the parent generation. Nothing else known of the life history of the species would suggest that it possesses an alternation of generations. Ants attacked the cynipids when they died after oviposition and only a single whole specimen, a male, was rescued for the collection. This, with galls of the two successive generations, are in my collections, distinctively labelled. I cannot say positively whether the reproduction is wholly or at any time parthenogenetic, though it is very likely that it is parthenogenetic at least part of the time. The one male in my net may have fertilized the fe- males, though I did not observe copulation.

Rhodites ignotus O. S.

Gall (Plate XLIII, Figs. 7-10). -Monothalamous. Very variable in shape and size. Spherical, irregularly rounded, reniform, single or more less confluent or two or three entirely coalesce thus forming an elongated mass of irregular shape. Clay brown, covered with a white farinaceous powder. Hard, woody, containing a rather large larval cell in the single gall and two or more cells in the coalescent ones. They are formed on the terminal twigs, leaves, or leaf-stalks, and as a rule are found in a cluster of from two to twenty. Measures from 4 to 15 mm. in diameter. On wild rose (Rosa blanda, R. nitida and R carolina).