Amphibolips confluentis

Cynips confluens

Cynips aciculata

Amphibolips aciculata

Andricus confluens

Spongy Oak Apple

Amphibolips confluentus

Florida

Cynipidae

Amphibolips

Quercus buckleyi

Kansas

Oklahoma

Texas

Quercus coccinea

Alabama

Arkansas

Connecticut

Delaware

Georgia

Illinois

Indiana

Kentucky

Louisiana

Maine

Maryland

Massachusetts

Michigan

Mississippi

Missouri

New Hampshire

New Jersey

New York

North Carolina

Ohio

Pennsylvania

Rhode Island

South Carolina

Tennessee

Vermont

Virginia

West Virginia

Wisconsin

Quercus falcata

Quercus ilicifolia

Ontario

Quercus marilandica

Iowa

Nebraska

Quercus rubra

Minnesota

New Brunswick

Nova Scotia

Prince Edward Island

Quebec

Quercus shumardii

Quercus velutina

Eastern forest insects

Cynipid galls of the eastern United States

Key to American Insect Galls

Insect-galls of the vicinity of New York City

Amphibolips confluenta (agamic)

Cynips confluentus

The largest galls in this country [Massachusetts] are commonly called oak-apples. They grow on the leaves of the red oak, are round and smooth, and measure from an inch and a half to two inches in diameter. This kind of gall is green and somewhat pulpy at first, but, when ripe, it consists of a thin and brittle shell, of a dirty drab color, enclosing a quantity of brown spongy matter, in the middle of which is a woody kernel about as big as a pea. A single grub lives in the kernel, becomes a chrysalis in the autumn, when the oak-apple falls from the tree, changes to a fly in the spring, and makes its escape out of a small round hole which it gnaws through the kernel and shell. This is probably the usual course, but I have known this gall-fly to come out in October. 


A Report on the Insects of Massachusetts, Injurious to Vegetation

Cynips confluens

Quercus rubra. Red Oak. Large, smooth, globular gall on the leaves, filled, when ripe, with a brown, spongy mass. Diameter about 1.5.

These galls are more than one inch, sometimes almost two inches in diameter. "They are green and somewhat pulpy at first," says Dr. Harris, "but when ripe, they consist of a thin and brittle shell, of a dirty drab color, enclosing a quantity of brown, spongy matter in the middle of which is a woody kernel about as big as a pea. A single grub lives in the kernel, becomes a chrysalis in the autumn, when the oak-apple falls from the tree, changes to a fly in the spring and makes its escape out of a small round hole which it gnaws through the kernel and shell. This is probably the usual course, but I have known the fly to come out in October." 

I am more inclined to agree with Dr Fitch who supposes that there are annually two generations of this fly. They are not rare around Washington, but I have never found them so abundantly as they seem to occur in other localities. On the first of June I found balls of this kind already ripened, measuring one inch and a half in diameter, of the usual drab color and somewhat greenish only at its base. One of them, which I opened contained a larva. On the 13th of June another gall was opened, it contained the perfect insect, but with wings yet wet and folded and evidently not quite ready to escape. 

On examining the specimens of this gall in my collection, I notice two varieties of it. The one, the surface of which is glossy, occurs on the smooth leaves of the red oak; the other, with a more opaque, almost downy surface, always occurred on tomentose leaves. I am unable to tell at present from what kind of oak the latter leaves were taken and hence, whether the gall is a different one or only a variety. I know that the same gall is said to occur on the black oak [Quercus velutina]; I found a similar one on the blackjack oak (Q nigra) and by cutting it open, obtained a gall-fly closely resembling C confluens.

[OS also describes Cynips aciculatus, reared from galls "answering exactly" Harris' description of C confluens but a distinct species based on adult morphology. C aciculatus was later synonymized with A confluenta.]

On the Cynipidae of the North American Oaks and their Galls

Cynips quercus aciculata 

Quercus tinctoria [velutina]. Black Oak. Large, round gall, broad and rounded at the top; surface smooth and glossy; shell thick, inside, a dense, brown, spongy substance, surrounding the kernel. Diameter upwards to an inch and a half. 

The specimens can be distinguished at once from the gall of C q spongifica, by their smooth, glossy surface and their subglobular or short-oval form, their basis being slightly attenuated, their top, on the contrary, being broad and rounded. Otherwise, their thick shell and their dense, brownish spongy substance reminds of C q spongifica. 

Mr. Walsh noticed their appearance in summer (about July). The gall-flies usually remain in the gall through the winter and escape in the spring; sometimes, however, especially when the weather in the fall is unusually warm, the flies leave the gall already at that season.

The synonymy of this species with C confluens Harris, supposed by Mr Walsh, is founded on the occurrence of their galls at the same season, and on the statement of Mr Norton about the agreement of C q aciculata with the original specimens of C confluens in Dr Harris' collection. But if Dr Harris' gall-fly really lives on the red-oak (Q rubra),  its great resemblance to C. q. aciciculata, occurring on the black oak (Q. tinctoria [velutina]) would no more be a proof of their identity, than the great resemblance of C. q. inanis and spongifica is of theirs. The two latter gall-flies, although almost perfectly similar in appearance, occur on different oaks and produce quite different galls. It may be that the true C confluens Harris, although closely resembling C. q. aciculata, produces on the red oak a gall, sufficiently different from that of the other species, to be distinguished by constant characters. The synonymy of both therefore, although probable, seems to require further confirmation.

It is also worthy of remark that both species of one group (C. q. aciculata and centricola) are produced by autumnal galls, and escape either late in the fall, or remain in the gall through the winter, whereas, the species of the other group all belong to vernal galls, the gall growing with the leaves and the fly passing through all the stages of its growth between the earliest spring and the end of June.

Additions and corrections to the paper entitled "On the Cynipidae of the North American Oaks and their Galls"

I have myself examined in all, at various times, some in the closet and some in the field, about a thousand specimens bred from or taken out of the gall of Cynips quercus aciculata--a species described by Osten Sacken from two specimens furnished by myself--and they were all beyond a doubt female. There can be no mistake here, because in this genus the male is distinguishable at a glance by its differently shaped and very much smaller abdomen; but to prevent the possibility of error, in most cases I ascertained the presence of the ovipositor. 

The trees from which I obtained the galls, or "oak-apples" as they are commonly called, on which I experimented, were an isolated and scattering group of 50 or 60 black oaks (Quercus tinctoria [velutina]), situated on a blue-grass prairie and without any other kind of forest-trees inter-mixed with them. The distance from this group to the nearest timber-land is about 150 yards. For many years I have procured from this source just as many Cynips q aciculata as I wanted, the galls occurring in prodigious exuberance there; and I had noticed three years ago that upon 6 or 7 of the largest black oaks in this group, on which the Cynips had hitherto been almost exclusively found, being cut down for fuel, the insect shifted its quarters to some other large trees which stood at the other end of the group, passing over a number of much smaller and younger trees lying in the intermediate space. One of these last large trees in particular was so badly infested by Cynips in 1863, that it must have borne from 400 to 500 galls. I have, however, occasionally found these galls elsewhere on quite young trees and even on saplings. 

These same galls occur on the black oak in two or three other localities near Rock Island, IL, but by no means so abundantly. They are, however, exceedingly local, and if all the black oaks within two miles of Rock Island were divided into groups of the same size as the one above described, I am confident that for one such group where the galls exist, certainly fifty and perhaps one hundred will be entirely destitute of them. I speak the more confidently on this point, because one of my favorite modes of collecting is by "beating," and because it is scarcely possible to "beat" an oak, where these large and conspicuous galls or "oak-apples" exist, without becoming aware of their presence. Another fact leads to the same conclusion. Every spring in the locality above referred to dozens and dozens of oak-apples of last year's growth may still be seen hanging on the trees, being almost invariably those from which the Cynips or its parasites have made their exit. In the winter of 1863-4 I have carefully looked for such oak-apples in many black oak patches where I had failed to find them in the summer, and could not discover a single one. Yet the trees being mostly leafless a single specimen would have been easily seen. On the same prairie mentioned above there is another group of black oaks, similar and similarly situated to the one that swarms with oak-apples, and distant from it about .25 mile. Yet a careful search in the winter failed to discover a single oak-apple hanging on the boughs. On the other hand I had no difficulty finding on the same occasion many of these galls still hanging on the trees in the two or three localities where I commonly find them in small numbers in the summer; nor in finding numerous galls of Cynips quercus inanis OS on the red oak still hanging on the tree. Yet that gall is not one-twentieth part so abundant as the one which produces aciculata. 

There are found near Rock Island the following species of oak, named in the order of their relative abundance, and on none of them, except the black oak, have I ever found the kind of gall which produces aciculata:--Quercus tinctoria [velutina], (black oak, by far the most abundant of any,) alba (white oak), rubra (red oak), macrocarpa (burr oak), imbricaria (laurel oak), and prinus variety discolor (swamp white oak.) Q coccinea (the scarlet oak) is believed by my friend Dr Fred Brendel, to be a mere variety of Q tinctoria, but it does not, so far as I am aware, occur in this vicinity. The identity of Q tinctoria and Q coccinea is an important fact, because Osten Sacken allows that his Cynips quercus coccineae, bred by him from Q coccinea, is scarcely distinguishable from C q spongifica, bred by him from Q tinctoria [velutina], and only separates them on account of the supposed distinctness of the galls from which the two insects were bred, and the supposed distinctness of these two so-called species of oak.

On May 17th, 1863, I visited the above described group of black oaks, and although their leaves were only about .75 grown, I noticed, in addition to several of last year's dry and brown oak apples, a very great number of green and freshly formed ones, many of which had attained their full size. On cutting a few of them open, I found the larva of the Cynips about .5 grown. Some of these galls had the terminal nipple attributed to the gall of spongifica by Osten Sack, some were smoothly spherical as the gall of aciculata was described by the same author, many had several nipples scattered irregularly over their surface, and 2 or 3 had as many as 12 or 14. The few I cut into had a rind or skin as thick as that of the normal gall of aciculata. I noticed a single specimen which was irregularly lobed like a common tomato. 

On May 24th some of the galls contained full-grown larvae, and on May 25th I found in several of them female pupae. On June 4th I opened several galls gathered May 24-5, and found in them some larvae and pupae, and one male and two female imagos of C q spongifica OS. Shortly afterwards I collected about 100 galls, as they were beginning to get ripe, and bred from them in all during the month of June, 6 male and about 20 female of spongifica, besides a great number of the Cynipidous inquiline or guest gall-fly, Synophrus laeviventris OS, and of two distinct species of parasitic Chalcididae belonging apparently to Callimome and Decatoma, and a single Bracon very near mellitor Say. Up to June 14 all the galls that produced spongifica flies were thin-shelled and of the type of the q coccineae. Such galls were then brown and ripe, whereas the more hard-shelled and thick-shelled ones were then more or less green and succulent. On June 14th, however, I bred a male spongifica from one of the latter description of galls, and many female afterwards from such galls; and I found that all the intermediate grades between the two types occurred in the galls that produced spongifica, some having a shell no thicker than writing-paper which wrinkled and collapsed and shrivelled up in drying, and some a shell as thick as ordinary cardboard, so as to retain their plump, apple-like appearance under the roughest usage; some again having a terminal nipple, some many nipples, and some none at all or next to none. The last spongifica (a male) came out June 18, and after that date no more made their appearance, nor after the last day of June any more inquilines or parasites except a single female Callimome(?) on July 23d. Of the whole number of galls somewhere about 1/2 remained on hand imperforated by any insect, those that were perforated having been from day to day picked out and thrown away. About the last of June, the thicker shelled galls having now become partially ripe and dry, I gathered 2 or 3 hundred more from the same locality, selecting of course those which had not been perforated by any insect. 

During the month of June I had endeavored to experiment on the mode in which these galls are generated, by enclosing the boughs of different species of oak with gauze-bags and placing therein freshly-hatched specimens of male and female spongifica. Owing to the mischievous propensities of certain unknown persons, the only fact I was enabled to arrive at was, that this insect when fed on white sugar, which it appears to eat freely, lives only 6 or 8 days. 

On July 16th I examined the group of black oaks, from the accessible boughs of which I had sometime before stripped all the galls. There were no new galls formed there, neither were there any subsequently formed there during the summer. Out of about 16 or 18 galls left on a particular tree, three or four of which I opened contained each a lively cynipidous larva in the central nucleus, and full one-half of the whole number were not perforated. On September 6th I opened two of the oak-apples gathered early in June, and found a black female pupa, apparently aciculata, in each. On Sept 17th and 18th I found in the same lot of oak-apples 7 female aciculata in the imago state, and during the month of October and the early part of November I bred very numerous imagos of the same, say from 50 to 60, all female. On October 25th I obtained three specimens from galls with a thinnish shell, and one from a gall with a shell as thin as paper with a distinct nipple at the tip. Of three others bred the same day from thick-shelled galls, one came from a gall with a terminal nipple, and the other two from spherical galls. On October 27, out of 11 or 12 female aciculata that came out, several came from galls with a terminal nipple and from galls covered with nipples all over, the rest from spherical galls. Other specimens continued to come out till November 16, and a single one after that date. Not a single parasite had made its appearance since July 23rd. On January 20, 1864, I cut into 30 or 40 of the remaining galls and found in them 9 aciculata female fresh and limber but dead, and 2 specimens dead and dried up, besides some dead and dried up parasites. 

Besides the locality above referred to, I reared in 1862 a male spongifica and several female aciculata from a different locality, the gall of the former gathered in the spring and that of the latter in the autumn and both found on q tinctoria [velutina]. 

From the above facts I draw the following conclusions:--

1st. Cynips q spongifica OS is identical with C q coccineae OS, as there are confessedly no distinctive specific characters of any importance, and the galls occur on the same species of oak (q tinctoria [velutina]) and are connected by all the intermediate grades. The spongy matter of the gall of q coccineae is said to be "whiter" than that of q spongifica, but I noticed several galls of aciculata, the spongy matter of which was in January, 1864, almost pure white. 

2nd C q spongifica OS occurs male female exclusively on q tinctoria [velutina], and emerges not later than June from galls that commenced their growth in the preceding month of May. 

3rd C q aciculata OS is a dimorphous form of C q spongifica OS, occurs exclusively in the female sex and exclusively on q tinctoria [velutina], and emerges from the last of September to the middle of November, and many of them not till the following spring, from galls that commenced their growth in the preceding May, which are undistinguishable from those which produce C q spongifica, the same kinds of gall from the same lot of trees, gathered at the same time, producing spongifica male and female in June and aciculata female in October and November, and nothing whatever but a solitary parasite in the intervening period. 

Suppose, for argument's sake, that aciculata and spongifica are distinct species. Then we are met immediately by the following difficulties:--1st. Is it likely that two distinct species of Cynips should produce, on the same species of oak, galls which are indistinguishable? I know of no such case in the whole Class Insecta. 2nd Is it likely that when spongifica, as above shown, is so local that it is only found in one station out of fifty near Rock Island, aciculata should select that particular station instead of some other one of the remaining 49? 3rd. If aciculata is a distinct species, then we are compelled to believe with Hartig in the existence of agamous species; ie of species that propagate from year to year ad infinitum without sexual intercourse with a distinct individual. I cannot believe that any species in the whole Animal Kingdom is uniformly agamous, for the simple reason that we should then have almost as many races, and finally species, as individuals. Monstrosities and remarkable variations, which with bisexual species are mostly eliminated by intercrossing with normal individuals, would then by the laws of inheritance be always intensified and exaggerated from generation to generation, and what was originally one homogeneous species would split up into an almost infinite number of distinct and sharply defined types.

That it may not be supposed that I approached this subject biased in favor of the conclusions above announced, it is proper to state that my original guess was, that there were two broods of this Cynips every year, the first a spring brood male female of the type spongifica, the second an autumnal brood, female only, of the type aciculata, generated in the ordinary course by the first brood, and in its turn generating by parthenogenesis the spring brood of spongifica in the following uear. It is scarcely necessary to add, that the facts utterly overthrow this hypothesis.

On Dimorphism in the Hymenopterous Genus Cynips: With an Appendix, Containing Hints for a New Classification of Cynipidae and a List of Cynipidae, Including Descriptions of Several New Species, Inhabiting the Oak-galls of Illinois

The True Oak Apple as it is popularly termed, (Quercus spongifica, Osten Sacken, occurs exclusively upon the Black oak (Quercus tinctoria [velutina]). It commences its growth in May, or as soon as the young leaves put forth, and reaches its full size in a few weeks. The central cell in which the larva resides becomes eventually hard and woody, but the space between that cell and the external skin or rind of the gall is always completely tilled by soft, drab, spongy matter. By the forepart or middle of June both male and female gall-flies (Cynips quercus spongifica OS) eat their way out of a certain number — say about a fourth part— of these galls, having developed into the winged state from the larva in the central cell. The hole by which the fly makes its exit is shown at Fig. 78 b. The remaining larvae lie dormant for more than two months, when they change into the pupa state, and subsequently about October eat their way out in the form of gall-flies (Cynips q aciculala, O. S.) closely allied to and yet quite distinct from those produced in June. Out of thousands of these autumnal flies examined by us, all were females with not a single male among them; and we have experimentally ascertained, by colonizing a number of these females upon isolated black oaks known to be not previously infested with oak-apples, that they cause oak-apples to be generated in the following spring upon such isolated Black Oaks. From Oak-apples produced in this manner we have bred two specimens of the spring form of Gall-fly (q. spongifica) which exists in both sexes, and five specimens of the autumnal form (q. aciculata) which exists exclusively in the female sex. Finally, treating these five autumnal specimens in the same manner, i. e. placing them upon another isolated Black Oak, we obtained galls in the following spring which produced two specimens of the spring form (spongifica), thus showing that the autumnal form sooner or later reverts to the spring form. Hence, as well as from other considerations, we may infer that the former is not a distinct species but a mere "dimorphous" female form of the latter; for otherwise, one form could not generate the other form. 

Galls and their architects

On October 29th and November 6th, 1864, I colonized a number of these agamous gall-flies, that I had bred myself from oak-apples, upon three different isolated black oaks, that I knew to have not been previously infested by these galls for many years back. Two of these trees were very large--say about 2.5 feet in diameter at the butt--and I placed the gall-flies upon one particular overhanging bough of each of them, and on no other part of the tree. The third tree was small--say 1 foot in diameter at the butt--and I placed the gall-flies on the trunk of this tree, at the point where the main branches took their origin.

On May 21, 1865, I examined all these three trees. The first large tree had no galls at all on it. The second large tree had produced four Q spongifica galls, partly on the very bough on which I had placed the gall-flies in the preceding autumn, and partly on some boughs that immediately adjoined it. I estimated that the portion of this last tree thus occupied by galls did not form more than one-twentieth of the whole tree; so that, even if we suppose that one or more wandering Cynips q aciculata had flown on to this tree from the neighboring woods in the preceding autumn--and this insect, coming out as it does so late in the year, flies as reluctantly and as dully as a plant-louse--the chances are about 19 to 1 that they would not have occupied the particular portion of it found to bear galls in the following spring. On the other had, as there certainly is not more than one-hundredth part of the black oaks growing near Rock Island that produce any oak-apples at all in any particular year, the chances are at least 99 to 1 against any particular black oak there, taken indiscriminately, bearing oak-apples in any particular year. Consequently, the compound chance of any particular black oak, taken at random from those growing near Rock Island, not only bearing them in a particular year, but bearing them exclusively upon a particular portion of its boughs, previously designated and forming only one-twentieth part of the entire mass of its boughs, is, according to the theory of chances, 1/2000; or in ordinary parlance, the chances are 1999 to 1 against such an improbable event happening. But these chances are founded on the supposition of the tree that was experimented on having been taken at random without any selection; whereas, instead of taking it at random, I exercised the greatest possible care in every instance, 1st, to select a black oak that grew a long way off from any other black oaks, and 2nd, to select one that I was familiar with and had watched for years, and knew not to have borne any oak-apples for several years preceding. 

The third black oak, visited on May 21, 1865--which was the small one--was absolutely loaded down with galls, and I estimated their number at 50 or 60 at least. At this early period all these galls were still small and immature, and it was necessary to leave them for a week or two upon the tree to ripen and mature.

On June 5th, 1865, I climbed the small gall-bearing black oak, and stripped it of every gall that I could see. From it I harvested only 18 normal spongifica galls, exclusive of 2 or 3 that had been destroyed by lepidopterous larvae, and about 40 specimens of a particular form of gall (Q pseudotinctoriae, Walsh) which occurs commonly but sparingly among the normal Q spongifica galls, and also, in a slightly modified type, upon red oaks infested by the Q inanis gall. For a long series of years this Q psuedotinctoriae gall has been a great puzzle to me; for, whether obtained from black oak or from red oak, although I have bred from hundreds of them, and have kept them on hand for years, I have invariably bred nothing from them but great numbers of a very large and very handsome Chalcis fly, belonging to the Pteromalides with concealed ovipositors, which I have never reared from any other gall, and a few stray specimens of such Chalcis flies (Callimome and Eurytoma) as I have bred also from the normal Q spongifica galls. My friend Baron Osten Sacken, to whom I had before this period communicated this peculiar form of gall, suggested that it was a true Q spongifica gall, modified by the action of the parasite that inhabited it; and the negative fact that I could never breed anything but parasites from it, after experimenting with hundreds of specimens in three or four different years, compels me to acquiesce in this most anomalous and, so far as I am aware, unprecedented conclusion. The gall in question never exceeds 0.85 inch in diameter, while the normal Q spongifica gall often attains a diameter of 1.75 inch, and is shaped like a normal gall, except that it is often studded outside with sharp prickle-like tubercles similar to those of the exotic gallae-tinctoriae gall--whence the name that I have given it. The central cell is round and about 0.2 inch in diameter, with an external crust which is only about 0.02 inch thick, instead of forming a dense woody mass as in the normal form. The external crust of the gall itself is similar to that of the normal gall; but, instead of its being connected with the central cell by homogeneous spongy matter, with a few subobsolete slender radiating filaments among it, as in that gall, it is connected with the central cell solely and exclusively by dense, opaque, coarse, whitish cottony fibers, radiating from the central cell, as in the Q inanis gall, but differing widely from those of that gall by being very much coarser, by being cottony instead of smooth, and by being placed so close together as to occupy the whole space between the cell and the external crust of the gall, instead of being separated from each other by very wide interspaces. On my cutting into 24 galls that remained unbred from, on this 17th day of March, 1869, out of the above-mentioned lot of about 40 Q pseudotinctoriae galls harvested June 5th, 1865, either of them were found to contain dead Pteromalidous imago already spoken of, seven what was probably its mature dead larva, one what was probably its mature dead pupa, one the pupal shell of a female Callimome, one a Eurytoma studiosa female, Say, and in six the tenant of the cell must have perished in early life, for in these six the central cell was empty. 

On the supposition of the peculiar character of the Q pseudotinctoriae gall being caused by the action of the large, Pteromalidous parasite that generally, but not always, inhabits it, and never inhabits the normal type of gall, it may be asked how it happens that this very same Q pseudotinctoriae gall sometimes produces the same species of green Callimome which is commonly bred from the normal gall, and occasionally a Eurytoma, which is also bred occasionally from the normal gall? I can only suggest that, in these two latter cases, the Callimome and the Eurytoma are parasitic upon the large Pteromalidous parasite, and that the peculiar character of the gall was determined in the first instance by the Pteromalidae. The Chalcididae are, to a much greater extent than is commonly supposed, secondary and not primary parasites.

From the 18 normal Q spongifica galls, obtained on June 5th, 1865, as specified above, from the small black oak, I bred on June 11th 1865, one C q spongifica female, and another female of the same type on June 14th, 1865. On cutting into the remaining 16 galls, on October 15th 1865, I obtained five living C q aciculata. Thus it results that q aciculata generates sometimes q aciculata and sometimes q spongifica. 

Lest it should be supposed that there was any reasonable probability of this small black oak having been attacked by any other gall-fly producing upon black oaks the Q spongifica gall besides those that I placed on it myself in the preceding autumn, it is proper to add here that it grew on the Bluffs, where black oaks are very scarce, and that I am quite confident that there is not another black oak within a quarter of a mile of it. So rare, moreover, are the galls Q spongifica upon the Bluffs, that in the course of six years' careful observation I have only noticed there three or four black oaks bearing these galls, and even then there were only from 3 to 6 on a tree; whereas on the sandy bottom land, which swarms with black oaks, these galls are comparatively quite common.

If, however, we choose to believe that the very same insect that produces the Q inanis gall also produces the Q spongifica gall, then the above mode of reasoning will not apply with such force; for the Q inanis gall, and the red oak on which it grows, are nearly as common on the Bluff as the Q spongifica gall, and the black oak on which it grows, are on the bottom land. Still, even upon this hypothesis, it is exceedingly improbable that Cynips q inanis should have attacked this particular small black oak in the spring of 1864; for 1st, I know that this tree bore no oak-apples for many years previous to 1865; 2nd, there were no red oaks growing anywhere within two or three hundrd yards of it, the few oaks that grew near it being either white oak or bur oak, which never produce either the Q spongifica or the Q inanis gall; 3rd, I noticed that, in the spring of 1866, this very same small black oak swarmed again with the Q spongifica gall, almost as abundantly as in the spring of 1865. Doubtless these galls had been generated by gall-flies that escaped from some of the galls before I harvested them on June 5th, 1865, or from green galls that had previously fallen off the tree on to the ground, as they will very often do in very great numbers when there is a high wind blowing, and be carried along the surface of the ground for hundreds of yards by the action of the wind; 4th, if we assume that the two galls that had produced C q spongifica June 11th and 14th, 1865, had been generated by C q inanis, and that only the five galls that produced C q aciculata October 15th, 1865, had been generated by the C q aciculata that I placed on the small black oak in the autumn of 1864, how does it come about that the Q spongifica gall is so very rare on those very Bluffs where the Q inanis is so common? Surely if C q inanis, bred from red oak, is capable of generating the Q spongifica gall on black oak, the Q spongifica gall ought to be as numerous on the Bluffs, in proportion to the number of black oaks growing there, as it is on the sandy bottom land, whereas it is no such thing. 5th, on the hypothesis of C q inanis generating Q spongifica galls, there again recurs the inevitable question "Why does C q inanis, if it is specificaly identical with C q spongifica, produce swarms of an autumnal dimorphous female--C q aciculata--on the black oak, and none at all on the red oak?" Or shall we take refuge in the anomalous hypothesis that one and the same bisexual species, variously known as C q spongifica sexgen and C q inanis sexgen, produces two such entirely different galls as Q spongifica and Q inanis upon black oak and red oak respectively, the same type of gall being always found upon the same species of oak; and that a distinct agamous species--C q aciculata--generates upon the black oak, galls which are utterly undistinguishable from those of C q spongifica upon the same oak, and which occur upon the same oak promiscuously intermixed with these last galls in scores of different localities, and yet that this agamous species never under any circumstances generates any galls at all--whether of the Q spongifica type or of the Q inanis type--upon the red oak? To such a supposition I can only oppose what, from long experience with galls of all kinds, I consider as an established axiom; namely, that the characters of the gall depend entirely upon the insect that makes it, and in no wise upon the plant, or the particular part of the plant, from which it grows. Consequently, I could as readily believe that a cow could produce sometimes a calf and sometimes a lamb, as that Cynips q inanis could produce sometimes a Q inanis gall upon red oak, and sometimes a Q spongifica gall on black oak. If it produced any gall at all upon Black Oak, instead of upon red oak which is its normal habitat, it would inevitably, in my opinion, produce a gall having all the characters of the Q inanis gall that is commonly found upon red oak.

I am well aware that much of the above reasoning will lack its due weight with the reader, because he has not, as I have, watched particular trees in a grove of Black Oaks swarming with oak-apples for year after year, while the neighboring trees bear none at all, or only a few scattering specimens, and because he has never seen, as I have twice seen with astonishment, that even a particular bough on a particular tree will bear numerous oak-apples for year after year, while the rest of the tree will bear none at all. Hence I have derived a profound conviction that the gall-flies that make these oak-apples, although they have full-sized wings, yet scarcely ever use them; whereas persons who are unacquainted with these insects would naturally suppose that they fly about the woods as freely as a bee or a butterfly. Out of the thousands that I have bred in my office, I never knew a single individual, whether of the vernal or of the autumnal type, to take wing at all; and only on one or two occasions, when I have been placing them upon oaks to experiment on the laws of their reproduction, have I seen one or two of them take wing, and then it would only fly a yard or two.

On June 11th, 1865, I gathered the four galls off the large gall-bearing Black Oak previously referred to. From these I bred no q spongifica at all; but on cutting into them on October 15th, 1865, I obtained therefrom three living C q aciculata.

On October 16th, 1865, having now in my possession two lots of living and lively q aciculata, one consisting of 5 females and the other of 3 females, that I knew to be generated by q aciculata of the preceding season, I determined to see whether they would all or any of them continue to generate q aciculata in the succeeding season, or whether, as had been the case with two of their predecessors, they would revert one or more of them to q spongifica. I therefore placed them, each lot by itself, on two fresh isolated black oaks, that I knew to have not been previously infested by these galls, for several years back at all events.

On May 31st, 1866, I gathered off one of these two black oaks, upon which I had colonized the 5 q aciculata in the preceding autumn, 5 q spongifica galls, four of them badly eaten by lepidopterous larvae, and only one in a perfect state. They were at this date too young and immature to gather with safety, but I feared to leave them longer on the tree on account of the caterpillars, which will very frequently eat away all the sponge and starve out the larva in the central cell. From this lot of 5 galls, generated by 5 C q aciculata in the preceding autumn, which 5 C q aciculata had themselves been generated in the autumn next but one preceding by the 8 C q aciculata that I had colonized upon another isolated black oak, I bred, on the 14th and 17th of the ensuing June, 2 Cynips q spongifica females. The remaining 3 galls produced nothing. 

The other isolated Black Oak, upon which I had 



On the group Eurytomidae of the hymenopterous family Chalcididae: with remarks on the theory of species, and a description of Antigaster, a new and very anomalous genus of Chalcididae

Amphibolips confluentus

Large, globular, more or less smooth outside and filled with a spongy substance in the center of which is a hard woody kernel containing the larval cell. From 1 to 2 in in diameter. When fresh, it is pale green, soft and succulent, with the contents whitish. Later in the season the shell becomes brown, hard and brittle, with the kernel woody and the spongy substance dark brown, but remaining soft. Confined to the leaves of the trees belonging to the red oak group. Common.

Amphibolips confluens

Cynips confluens
Cynips aciculata
Cynips quercus aciculata
Amphibolips aciculata
Andricus confluens
Amphibolips confluens
Amphibolips confluentus
Amphibolips confluentis

[Beutenmueller gives no description of A confluenta itself, only the form spongifica, which he treats as the same species:]

Gall. On the leaves usually from a vein or the petiole on red oak (Quercus rubra), scarlet oak (Quercus coccinea), quercitron or yellow oak (Quercus velutina) in May and June. Globular or nearly so, smooth, shining or opaque with a thin outer shell. Internally filled with a juicy white spongy substance and with a large, hard, central larval cell. When fresh the gall is green, and light brown when old and dry, with the internal spongy substance dark brown. Diameter, 25 to 50 mm.

Habitat: Canada; New England and Middle States, south to GA and west to CO.

This well-known gall is very common and hundreds may often be found upon a single tree. It makes its appearance early in may, as soon as the leaves put forth, on different kinds of oaks belonging to the red oak group, and is fully grown in a few weeks. It is popularly known as "oak-apple" or May-apple, owing to its superficial resemblance to a small apple. From a certain number of the galls emerge, by the middle of Jun, both male and female gall flies. The gall-flies which emerge in October or the following spring are all agamous females.

The species of Amphibolips and their galls

Amphibolips confluentus 

Cynips confluentus
Cynips confluens
Cynips quercus spongifica
Cynips quercuscaciculata
Cynips quercuscoccineae
Amphibolips coccineae
Amphibolips spongifica
Amphibolips confluentus

A globular gall found attached to leaf by small portion. Monothalamous; larval cell surrounded by brown spongy mass, and that by a rather smooth thickened wall. Pale green and soft while fresh, turning brown and brittle. 2-4 cm in diameter. Common on black, red, and scarlet oaks. Begins growth about May. Males and females emerge in June. Some females remain until October (C aciculata OS) A good example of dimorphism.

Insect galls of Springfield, Massachusetts, and vicinity

Amphibolips confluens

Oak apples, intervening substance is spongy, size large

Globular, smooth, shining or opaque leaf gall, internally a juicy, white, spongy substance and a large central larval cell, green, turning with age to light brown, diameter 2.5 to 5 cm, usually on a vein or petiole, on Q rubra, coccinea, and velutina in May and June.

Amphibolips confluens

B.D. Walsh (1864) had reported in great detail the discovery of two very different forms of adults, one agamic and the other bisexual, emerging at different times of the year from very similar if not identical galls of Amphibolips confluens. The work was undoubtedly exact as far as it went and, if it covers the complete life cycle of the species, it furnishes the first completed record of alternation. But Walsh, though he attempted to control the insects by confining them in nets placed on the trees, was unable to discover oviposition and it is not yet satisfactorily shown that the complete life cycle of the species has been discovered. 

Life histories of American Cynipidae

Amphibolips confluentus (Harris)

Galls at Ithaca, NY, contained full-grown larvae on July 14, 1908, when collected, pupae on August 1 and adults September 12 when 86 specimens, all females, were cut out of the galls. A gall at waterport NY contained a pupa August 14. Galls at Manistee, MI, contained adults when opened September 20. At Miller, IN, galls just turning brown were gathered on June 3, 1911, then containing full-grown larvae which had transformed into adults by Sept 16. Flies emerged Nov 21 1918, from galls on Quercus velutina from Lyme CT. Brodie collected galls on Q coccinea at Toronto in October and producers emerged Nov 10 1892, all females.

Field notes on gall-inhabiting cynipid wasps with descriptions of new species

Amphibolips confluentus

Leaf galls
Similar [to Amphibolips spongifica] but the adults, all females, emerge in Nov. Probably an alternating generation of the above but the life history needs further study.

Cynipid Galls of the Chicago Area

Amphibolips confluenta (Harris)

Cynips confluentus Harris
Cynips aciculata  Osten Sacken

Range: Toronto to Ill, IO, KS; MA to VA. Gall on various red oaks.


Hymenoptera of American north of Mexico: Synoptic catalog (1951)

Amphibolips confluenta

Quercus coccinea, falcata, ilicifolia, marilandica, rubra, texana [buckleyi], velutina
Leaf galls, integral
Spongy Oak Apple. Aborts the development of the leaf. Agamic females emerge in October. 

[Photo caption] Spongy Oak Apple. On Q velutina. Also on Q coccinea, rubra, falcata, marilandica, texana. Galls in NY contained pupae Aug 1 and adults Sept 12. Adults emerged Nov (CT), Toronto Nov 10--all females.

Amphibolips confluenta

The Large Oak Apple gall, occurs from southern Canada to Virginia. It produces galls on the leaves or leaf petioles of various oaks, principally red, black, and scarlet. These galls are quite large, from 12 to 50 mm in diameter, and greenish to brownish in color, depending on age.

Amphibolips confluenta (Harris) 

Cynips confluentus
Cynips aciculata

Range: Mass, Ont to VA, west to IL, IO, KS

Produce leaf galls on red oaks

Catalog of Hymenoptera in America north of Mexico

Amphibolips confluens 

Heterogony or alternation of generations in Cynipini was discovered, independently, in United States by Bassett (1873) and Riley (1873). However Osten Sacken (1861) suspected alternation of generations in Callirhytis quercusfutilis (Osten Sacken, 1861) and Amphibolips confluens (Harris, 1841). Later, Walsh (1864) supported the idea about alternate generations in Amphibolips confluens, but no direct experiments were carried out and so first “clear” demonstration of a life cycle in Cynipini is due to Bassett (1873) (after Wehrmaker, 1998). 

In some cases, studies on life cycles were taken by some specialists with scepticism, as in the case of Walsh’s studies on Amphibolibs confluens in United States.

[A table appears that lists Amphibolips confluenta's sexual form as "known, not named ?", referencing Osten Sacken 1861]

Current state of knowledge of heterogony in Cynipidae (Hymenoptera, Cynipoidea)

This species is the most commonly observed cynipid gall in the eastern US, and readily recognized by its size, placement, and spongy interior. There is substantial taxonomic confusion in the distinction between A confluenta and A quercusspongifica. Osten Sacken described three species--aciculatus, spongifica, and coccinea--which he distinguished based on host species, gall morphology, and emergence timing. Walsh subsequently conducted a large-scale rearing program of galls from Quercus velutina at a single site in Illinois, all fresh in May. He found that the galls differed morphologically between two endpoints, and that the emergence timings clustered clearly into two periods: sexgen adults in June, agamic females from September to November, with some emerging in the subsequent spring. However, he observed that both gall morphologies were found in both emergence periods, and noted a range of intermediate forms suggesting there was no consistent distinction to be drawn between them. He concluded that they were alternating generations of the same species, of which the agamic females in the fall laid unfertilized male eggs and the mated sexgen females in the summer laid female eggs, both of which hatched in the subsequent spring. 

Walsh later apparently conducted experiments that he and Beutenmuller took as definitive confirmation of this hypothesis, which he published, synonymizing quercusspongifica as the sexgen form of Amphibolips confluenta. His experiments involved placing agamic females reared in October onto trees he understood to be isolated and not previously host to Amphibolips. While his host trees were not isolated from oviposition by other wasps, if his assumption that no other oviposition is remotely likely is accepted, Walsh's results show that oviposition by agamic wasps in the fall produces identical galls the following spring from which emerge both sexgen females in June and agamic females in the fall, and that these agamic females in turn lay eggs that produce sexgen females in the following spring. It is noteworthy that Walsh's experiments produced no males even from the sexgen galls, though this may be a coincidence given the small numbers of wasps he successfully reared. Further, Walsh was never apparently able to record the results of oviposition by sexgen females (perhaps due to this lack of males?). 

Kinsey considered Walsh's research inadequate because no oviposition was documented, and Weld treated spongifica and confluenta as distinct species pending "further study" but noted they are "probably" synonyms. 

The hypothesis Walsh put forward is highly unusual relative to every closed life cycle published since. There are several known cases in which sexual generations become facultative or discarded entirely, with agamic females emerge from agamic galls and laying eggs that become agamic females inducing agamic galls. However, in all such documented cases, the sexual generation gall is very different from the agamic gall, sometimes even occurring on a different host section. In Walsh's hypothesis, the sexgen and agamic galls are indistinguishable in host, phenology, and appearance. 

Additionally, by analogy with related species, it is surprising that the sexgen females emerging in June would oviposit in tissues during the growing season but not take advantage of the plant's growth to create a new gall until the following spring. [Amphibolips quercusinanis](https://www.gallformers.org/gall/582), for instance, is a sexual generation gall similar to quercusspongifica that emerges and oviposits in June. Unconfirmed genetic evidence suggests that the eggs it lays immediately cause the subsequent growth of galls of [Amphibolips cookii](https://www.gallformers.org/gall/1143), which produce agamic females in the fall which oviposit in buds before winter. Assuming that Walsh's evidence is true to the extent he was able to confirm, it is conceivable that this species produces another, distinct agamic gall in the fall.

On red-group oaks, A confluenta/quercusspongifica is commonly confused with A quercusinanis, which also occurs on leaves in the spring but which has a uniformly smooth exterior with distinct spots, A quercusostensackenii, which is much smaller and doesn't distort the host leaf, and A cookii, which occurs on buds in the fall and has larger spots and thicker walls. A confluenta typically has a bumpy surface. The most definitive way to distinguish it is to note the spongy interior; A quercusinanis and A quercusostensackenii has a stringy, empty interior, while A cookii has thick, succulent fibers. 

Some specimens that otherwise resemble A confluenta do have spots. This may represent a different species but is more likely a host- or generation-related variation (these spotted variants are typically but not definitively or exclusively associated with Quercus buckleyi, shumardii, pagoda, and velutina).

A confluenta/quercusspongifica early in the spring can also be confused with Dryocosmus quercuspalustris, which also forms green, spherical, integral leaf galls that distort leaves. The galls are easily differentiated by their internal structure, which can be observed by shining a bright light through the gall or but cutting it open. D quercuspalustris has a loose larval cell freely rolling around in an otherwise empty chamber. D quercuspalustris galls are much smaller and differ subtly but distinctly in texture. A confluenta/quercusspongifica galls almost always completely deform their host leaves, to the extent that they are often barely visible, while D quercuspalustris galls may seem to almost completely displace the leaf (especially early in leaf out) or have minimal effect on its overall structure (later in the season). 

Gallformers ID Notes