Neuroterus umbilicatus agamic form

GALL. — Small, separable, saucer-shaped. Each cell monothalamous. Up to 1.0 mm. in diameter, strictly circular, flattened, centrally depressed, with a low rim, a minute point in the center of the depression; light green, becoming brown; rather densely covered with short hairs; attached by rather a broad point, but quite easily separable, hardly at all imbedded in the blade, but indicated on the upper surface of the leaf by a slight papilla surrounded by a considerable circle of discoloration. Internally entirely hollow, without a distinct larval cell. On the under surfaces of white oaks, commonly on Quercus bicolor (the type variety), recorded from Q. michauxii (acc. Felt), Q. macrocarpa (acc. Jarvis), and Q. stellata (Patterson coll.). Figs. 40, 41.

RANGE. — Ontario (Jarvis). Massachusetts: Boston (in Clarke coll.); Forest Hills (Kinsey coll). Connecticut: Waterbury (Bassett); New Haven (Viereck). New York: New York City, Staten Island (Beutenmuller) ; Barrytown (Bassett in coll. Mus. Comp. Zool.); Hudson Falls, Mt. Kisco, Sea Cliff (Felt). New Jersey: Ft. Lee (Beutenmuller); Broadway (Kinsey coll.). Pennsylvania, Illinois (Beutenmuller). Mississippi: Pickens (Felt). Texas: Austin (Patterson coll.) . Probably thruout the eastern half of the United States.

The gall of this species is very common, and a familiar object to all who have hunted galls in the northeastern part of the United States, but the insect is so difficult to rear that, as far as I know, no one has yet accomplished it. Bassett’s type material was obtained by cutting mature adults from galls and by capturing them as they were flying about the oak trees to oviposit. The galls of this agamic form are found on the leaves in late summer, but do not mature until very late in the fall as the leaves are falling. Most of the galls have by then become detached from the leaves, and are soon lost on the ground. By sifting the soil, sand, and leaf-mold, Bassett succeeded in the spring in obtaining galls which contained living wasps. The growth of the insect is probably very dependent upon moisture and temperature conditions of the sort found on the ground thruout the winter months, and the minute galls, with their thin walls, dry out very soon after collecting, explaining the difficulties in breeding the insect. Bassett found insects of this species in numbers over an oak, on a warm spring day, ovipositing in the buds of the tree. He further states that ‘In the latter part of May and the beginning of June the young galls were nearly full grown and as abundant as ever before.” This last must apply to a spring generation, for the galls of the agamic form are not mature until September or later; and inasmuch as Bassett failed to differentiate the spring galls it would appear they are similar to the agamic galls, similarly placed on the leaf. The insect of the spring form may be agamic (as with the closely related saltatorius), or bisexual as with other species of Diplobius, and it will be interesting to determine this definitely. These data have been published for twenty-three years, but have apparently been overlooked as a record of heterogony.

The type variety is on Quercus bicolor, and the records for other hosts will prove to represent distinct varieties. The type locality is in Connecticut. The Ontario, Illinois, Mississippi, and Texas records will undoubtedly represent as many distinct varieties. The oaks, Q. bicolor, Q. macrocarpa, and Q. stellata, belong to a single group, but Q. michauxii belongs to the group of chestnut oaks. If the last record proves correct, the insect would appear to occur on species of both white and chestnut oaks over all of the eastern half of the United States, with a possibility of upward of 80 varieties. Mr. Frank A. Leach has collected a very similar but slightly different gall on Q. lobata and Q. douglasii from localities in central California; it is possible these will prove varieties of this species, extending its range over the whole of the United States.

The monothalamous, rather separable gall, connects this species with saltatorius, and the insects of the two are so nearly alike that they can hardly be separated. Here is another case of physiologic species, and a rather remarkable instance inasmuch as the galls of the two are very distinct. When we have discovered a larger number of varieties of each species, we may be able to perceive the specific characters more clearly.

Neuroterus umbilicatus

Quercus alba, macrocarpa
Leaf galls, detachable
Fig 217, 314. Cup-shaped with inrolled edge 3-4 mm in dia, covered with short whitish hair, on under side in fall.

Quercus bicolor
Leaf galls, detachable
Fig 217, 314. In numbers on under side covered with short stiff hairs. Easily detached and leave a dead spot on leaf.

[Photo captions]

217. On Q alba. Also on Q bicolor. Neither Beutenmueller nor the writer has been able to rear it. Perhaps the good galls (ie those without guests) drop early. See also Fig 314.

218. Cup-shaped with inrolled edge, 3-4 mm in dia, covered with short whitish hairs, on under side of leaf of Q alba in the fall.

[Undescribed species tentatively assigned to Neuroterus umbilicatus based on later report of this species on Q chapmanii by Price et al]

Quercus chapmani
Leaf galls, detachable
Spangle with an inrolled pubescent edge, 1 mm in dia, in numbers on the under side of leaf in the fall.

Neuroterus umbilicatus [generation inferred from phylogeny]

Galls on Quercus bicolor, agreeing with Bassett specimens, were collected at Washington, D. C, on September 23, 1923. No adults were reared, as some of the galls at least still contained larvae June 1, 1924. In late October, 1924, William Beutenmueller collected galls at Tenafly. N. J., and sent some to the writer for rearing. Up to January 1, 1926, he had reared nothing from the thousands of galls in his breeding cages, some indoors and some out, nor has the writer succeeded in rearing the adults. Galls were also seen at Ithaca, N. Y.

Neuroterus umbilicatus, n. sp.

The galls of this species are found in great numbers on the under surface of the leaves of Q. bicolor. Four or five hundred have been counted on a single leaf. They are small, circular, flattened and concave, with a minute conical elevation in the centre of the concavity. They are about .07 of an inch across and .05 in depth, and the pit is only .04 across. Beneath the conical elevation lies the minute larval cell. Except the concavity described, which is smooth, the surface is covered with short, stiff hairs, much like the under surface of the leaf. The galls are easily detached, but leave an indentation which is seen as a flattened elevation on the upper surface of the leaf. The peculiar form of these galls suggests the trivial name.

I collected these galls in countless numbers for many years, and made numerous unsuccessful attempts to rear gall flies from them. Flies in vast numbers were bred from them, but all bore the unmistakable marks of cynipideous parasites. These repeated failures led me to wonder if there might not be, after all, species bearing all the characters of the parasites that were true gall makers. It is true that I knew of no such species, and I did not forget that proof of this negative sort and hardly less in amount led Dr. Fitch to publish a winged parasite as the originator of his Cynips ficus galls, which, later, Dr. Walsh discovered were produced by the subapterous Biorhiza forticornis. I, too, had reared millions of parasites from the galls Neuroterus floccosus B. before a single gall fly was discovered. Visiting on a warm morning in Spring an oak that had for years furnished these galls in abundance, I found a species of Neuroterus laying eggs in the buds of this tree. Busy capturing specimens from the low branches of the tree it was sometime before I discovered that my clothing was covered with flies of the same species. Having but a few minutes left for collecting, I was only able to collect some thirty individuals from the buds and my clothing. I left unwillingly, to return in the afternoon. By afternoon the weather had turned cold and not an insect of any kind could be found.

I made visits later and on more favorable days, but no flies were seen. On one of these visits I took up a quantity of sand and leaf-mould under the tree, and sifting it carefully found many empty galls and two that contained perfect living gall-flies. One of these I destroyed in opening, the other proved to be identical with those captured a few days before, and from it the above description is, for the most part, drawn.

In the latter part of May and the beginning of June the young galls were nearly full grown and as abundant as ever before. At this time I had in my breeding boxes, in damp earth, galls of this sort gathered the Autumn before, and from them were appearing parasites in considerable numbers. Visiting the tree at this time I found from one to five of these flies actively at work among the umbilicus galls. I cannot say that I actually saw them stinging the galls, but we may reasonably suppose they were doing so, and it is easy to understand why so few gall-flies are so produced from the almost countless number of galls of this and some other species. I have seen parasitic hymenoptera stinging, but not often. My favorite oak has recently been cut down and a railroad siding covers the stump, but I hope to find another as good on which to follow up my investigations.

Neuroterus umbilicatus

Gall. (Plate XIII, Fig. 7.) In great numbers on the underside of the leaves of swamp white oak (Quercus platanoides [bicolor]) in August and September. Monothalamous. Small, circular, flattened and concave, with a minute conical elevation in the centre of the concavity. Beneath the conical elevation lies the minute larval cell.Brown and covered with minute hairs. The galls are easily detached, but leave an indentation which is seen as a flattened elevation on the upper side of the leaf.Diameter, 1 to 1.50 mm.

Habitat. Canada (Ontario); Connecticut; New York; New Jersey; Pennsylvania; Illinois.

Neuroterus umbilicatus (Bassett 1990)

Hosts: Quercus chapmanii

[Asexual generation detachable leaf gall found in the spring. First record in FL.]