Neuroterus niger Gillette, 1888

Synonyms: Neuroterus nigrum Gillette (1888: 218), females and galls. Revised spelling by Dalla Torre and Kieffer (1902: 51).
Neuroterus papillosus Beutenmueller, 1910, syn. nov.
Neuroterus perminimus Bassett, 1900. Synonymized by Beutenmueller (1910: 121), and treated as a variety of N. niger by Kinsey (1923: 48), but synonymy ignored by Weld (1951) and later authors; syn. nov.
Kinsey (1923) described 5 additional varieties of N. niger, all inducing integral leaf galls. Four we consider as synonyms: Neuroterus niger var. arizonicae Kinsey, 1923 (asexual generation, Arizona, on Q. arizonica), syn. nov.; Neuroterus niger var. grisea Kinsey, 1923 (asexual generation, Texas, on Q. grisea), syn. nov.; Neuroterus niger var. nigripes Kinsey, 1923 (asexual generation, Texas, on Q. sinuata var. breviloba (=Q. breviloba) and Q. stellata), syn. nov.; Neuroterus niger var. pattersoni Kinsey, 1923 (asexual and sexual generations, Texas, on Q. sinuata var. breviloba (=Q. breviloba) and Q. stellata, respectively), syn. nov..

The fifth variety described by Kinsey is Neuroterus niger var. alimas Kinsey, 1923 (sexual generation, Texas, on Q. virginiana) that was still considered as form of N. niger by Burks (1979). According to Kinsey (1923) this variety induces a sexual generation spring gall, while the other four varieties induce autumn asexual generation galls. Moreover, N. niger var. alimas is the only variety associated with section Virentes oaks while the other four are on section Quercus oaks, and as mentioned in the Introduction, no Nearctic cynipid species are shared across the oak sections (Abrahamson et al. 1998a, 2003; Stone et al. 2009). Hence biological information suggests that N. niger var. alimas is a species distinct from N. niger (sensu Gillette 1888) and the other four of Kinsey’s varieties. Kinsey (1923) described N. niger var. alimas based on one female (holotype – lost) and 13 males and gave no detailed morphological description for this variety. Thus, there is no morphological evidence for synonymisation of N. niger var. alimas to N. niger while at the same time it cannot be treated as a valid species so Melika et al. (2021) moved it to nomen dubium.

Gall. The asexual generation gall is described by Gillette (1888) and are small blisters integral to the leaf blade (Fig. 181).

Biology. See Gillette (1890), Beutenmueller (1910), Kinsey (1923), and Weld (1926) for the biology of one or both generations. The minute, integral leaf galls of the asexual generation have been recorded on Q. macrocarpa. Galls became evident in Edmonton in August and matured in September. This species represents a rare case where males are present in the asexual generation. Males of the asexual generation comprised a tiny fraction of the cynipids reared from asexual generation galls, with only 62 males reared from gall collections made in Edmonton during 2004- 2006, as opposed to 20979 females. In addition, most males were reared in the autumn (October-December) of the year of gall formation, whereas almost all females emerged in April-May the following spring after gall formation. Thus, most males were temporally isolated from ovipositing females and therefore essentially functionless. This is similar to Patterson’s (1928) discovery of functionless males of the asexual generations of Neuroterus contortus (Weld, 1921) and N. quercusrileyi (Bassett, 1881). In his study, males and females co-occurred, but they appeared unwilling to mate under laboratory conditions. Galls of the sexual generation are on Q. alba, Q. bicolor and Q. macrocarpa (Gillette 1890, Burks 1979, Digweed 2010). We observed that clusters of galls (e.g., on one catkin) often produced adults of only one gender. Galls were visible in Edmonton in May, with adults emerging in late May or early June. Sexual generation females were observed ovipositing mostly on the undersides of leaves and often on leaves that were on long shoots and/or that were not yet fully mature.

Distribution. In the USA the asexual generation has been recorded from Massachusetts, Michigan, Wisconsin, Iowa (Burks 1979), Illinois, Indiana, New York, New Jersey, Pennsylvania, Ohio (Beutenmueller 1910); Arizona, Texas (Kinsey 1923), and Alberta and Manitoba in Canada. The sexual generation has been recorded from Illinois (Weld 1926), Iowa (Burks 1979), and TX (Kinsey 1923) in the USA and Alberta in Canada.

Neuroterus nigrum n. sp.

Galls: The galls are little pimples about 2 mm in diameter on the surface of the leaves and show equally well from above and below. There are usually a large number on a single leaf. The galls appear late in August but the flies do not emerge until the following summer. Few of the these galls were noticed in Michigan, but they are very common about Ames Iowa. My specimens were reared from the leaves of the burr oak, but in a number of instances I have taken galls that seem exactly similar on the leaves of the white oak, Quercus alba.

Undetermined species [tentatively associated with N niger. N niger isn't otherwise listed in this source.]

Cells separate but in more or less definite rows along the midrib or a main vein, more prominent on upper side, a faint papilla in center below, round in outline, about 1.5 mm. in diameter. Exit hole on the lower surface. On Q. alba in the fall.

Neuroterus niger

Quercus alba, muehlenbergii, stellata
Leaf galls, integral
Round parenchyma thickenings, 2 mm in dia, more prominent above, nipple below, along main veins in fall.

Quercus macrocarpa
Leaf galls, integral
Parenchyma thickening in the fall.

[Photo caption]
On Q alba. Also on Q stellata (teste the Thompson collection). Agamic females emerge the next spring.

Neuroterus niger var arizonicae Kinsey

Quercus arizonica
Leaf galls
Integral
Similar to howertoni above

Neuroterus niger

Globose or blisterlike, monothalamous leaf vein swellings more distinct on the upper side and with a minute nipple on the lower surface, diameter 1 to 1.75 mm, on Q. alba and Q. macrocarpa.

[Felt reproduces Beutenmuller's drawing]

Neuroterus niger variety niger Gillette
agamic form

Neuroterus nigrum
Neuroterus niger

GALL. — Rather rounded, somewhat elongate, with well-defined boundaries, without a central point on the upper surface. On Quercus macrocarpa.

RANGE. — Iowa: Ames (Gillette). Illinois: Algonquin (Nason). Michigan: Lansing (Gillette). Possibly confined to a smaller area about Ames, Iowa.

Gillette stated that the galls of this agamic generation appear late in August; he collected his galls on October 20, 1887 ; adults emerged on May 10, 1888. The Thompson material also over-wintered in the galls, emerging about the middle of May. Beutenmuller’s further data appear to be derived in part from variety perminimus which he considered a synonym of niger.

Neuroterus niger variety arizonicae, new variety
agamic form

GALL. — Rather circular, slightly elongate, with only an indefinite trace of a point on the upper surface; the boundaries very indefinite, especially on the under surface; on Quercus arizonica.

RANGE. — Arizona: Bisbee, Fort Huachuca, Whetstone, Salford, Globe, Santa Catalina Mountains (Sabino Trail). New Mexico; Alamogordo. Probably thru Arizona, New Mexico, and adjacent Mexico, wherever Q. arizonica occurs.

The insects probably do not emerge until late in January or February.

Neuroterus niger variety griseae, new variety
agamic form

GALL. — A little more elongate than circular, with very poorly defined boundaries and not much thickening of the blade, perceptible mostly because of a discoloration, less perceptible on the under surface. On Quercus grisea.

RANGE. — Texas: Fort Davis. New Mexico: Hillsboro. Probably occurs in West Texas, New Mexico, and adjacent Mexico (and Arizona?).

The insects probably did not emerge from the galls until early in the spring after collecting. The galls are indistinct and not at all noticeable; the insect is clearly different from other varieties; so it seems worth describing even tho the type material is not abundant.

Neuroterus niger variety nigripes, new variety
agamic form

GALL. — About circular, slightly elongate, very slightly larger than pattersoni, with less well-defined boundaries and with a distinct central point on the upper surface. On Quercus stellata and Q. breviloba (fig. 34, 42).

RANGE. — Texas: Austin, Leander.

Larvae were in the galls I collected on December 4, 1919. Dr. Patterson has made detailed observations on this species, finding that the young galls were evident on July 28, 1921, Indiana University Studies maturing-about the first of December ; he secured adults about the first of March, 1921. Dr. Patterson has bred galls from both Q. stellata and Q. breviloba, and I cannot see any differences between the two lots of material. Another variety, pattersoni, also occurs at Austin on both of these oaks, but the insects and galls are always distinguishable. Evidently two faunal areas, meeting at Austin, have effected an isolation which is not accomplished by the two hosts.

Neuroterus niger variety pattersoni
agamic form hiemalis, new form

GALL. — Probably quite similar to that of the bisexual generation. On Quercus breviloba.

RANGE. — Texas: Austin (Patterson coll.).

The occurrence on the two different hosts is not remarkable; probably both forms occur on both stellata and breviloba at Austin. This is true of variety nigripes, and care must be taken to distinguish pattersoni and nigripes; the characteristics in the descriptions are quite constant guides to both insects and galls.