Cynips inanis

Callaspidia confluens Fitch, non Harris

Callaspidia confluenta Fitch, non Harris

Cynips quercus inanis

Amphibolips inanis

Cynipidae

Amphibolips

Quercus rubra

Alabama

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Indiana

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Key to American Insect Galls

The species of Amphibolips and their galls

Insect-galls of the vicinity of New York City

Cynipid galls of the eastern United States

Amphibolips quercusinanis (sexgen)

Callaspidia confluenta, Harris [Fitch believed he was referring to a species, now Amphibolips confluenta, already described by Harris, but understood to be a distinct species by Osten Sacken shortly after.]

Large smooth globular galls resembling apples, growing on the lower veins on the under side of the leaves of the red oak.

There are probably two generations of it annually, for early in June the galls are found upon the trees grown to their full size, which varies from an inch to an inch and three-quarters in diameter. Their attachment to the leaf is so slight and brittle that when the leaves are agitated with a strong wind numbers of them break off and fall, so that the ground under particular trees is copiously scattered with them, even when they are but half or two-thirds grown, the latter part of May. They then resemble large nice smooth gooseberries, being of a lively pale green color, freckled with large blackish or purplish brown dots, and clear and semi-transparent when held between the eye and the light, with an opake cloud-like spot in their center. Cut open, this central spot is seen to be a pale greenish yellow ball the size of a pea, with numerous white threads beautifully radiating from its surface to the outer wall, and holding this ball in its place in the otherwise vacant cavity. On cutting this ball asunder it is found to be very juicy and white internally, with a round cavity in its center, in which lies a small plump white maggot, curved into the shape of a crescent, and lying motionless and without any signs of life. The exterior wall is 0.05 thick, or about the thickness of the rind usually taken from an apple when it is peeled, and of a similar succulent juicy texture.

Fifth report on the noxious and other insects of the State of New York

Cynips quercus inanis (Syn C confluens Fitch, non Harris)

Quercus rubra. Red oak. Large, smooth, globular brownish-yellow gall, attached to the underside of the leaves, inside with whitish, delicate filaments radiating from the kernel to the shell. Diam about an inch.

Very like gall No. 1 [Cynips confluens, now Amphibolips confluenta] at first glance, but smaller, the specimens in my possession measuring an inch or a little more in diameter. It is also fastened to the leaf by a small point on its surface. The outside of this gall shows no other difference from the oak-apple of the red oak but the size. The inside on the contrary distinguishes them at once; instead of the spongy, brown mass with which the other gall is filled, this one is almost empty, the kernel being kept in its central position by a certain number of whitish filaments which radiate from it to the shell. 

Habitat: DC

On the Cynipidae of the North American Oaks and their Galls

Cynips quercus inanis

Q coccinea. Scarlet oak? Large, more or less round gall, not attenuated towards the basis; surface glossy; shell thin and brittle; on the inside whitish filaments radiating from the kernel to the shell. Diameter about an inch. 

I have found this gall more than once on young trees, belonging either to Q coccinea or Q rubra. (the leaves were elongate, cuneate at the basis and hardly or, at least, not deeply, sinuate; this is, I believe, one of the varieties of the scarlet oak.)

Among the specimens of my collection, I find a number of galls, collected in one locality and somewhat different in shape from the typical specimens of C q inanis. The latter are more or less globular, the leaf being, so to say, the tangent of the globe. There is no distinct point or nipple on the top. The other gall, on the contrary, is somewhat lemon-shaped, being attenuated at its basis with a corresponding elongation, ending in a minute nipple, at the opposite end. Its color is more brownish than that of C q inanis; on the inside, I did not detect any difference between both galls. The tree is also either the red or the scarlet oak.

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

Amphibolips inanis

Shape like the preceding [Amphibolips confluentus] but considerably smaller. Almost empty, the larval cell being kept in position by radiating filaments. Green and soft when young, brown and brittle when dry. On leaves of scarlet (Quercus coccinea) and red oak (Q rubra).

Amphibolips inanis (Osten Sacken)

Callaspidia confluenta
Cynips quercus inanis
Cynips inanis
Amphibolips inanis

Gall. On the leaves of scarlet and red oak (Quercus coccinea and Quercus rubra) in May and June. Bright green, sometimes with darker spots. Globular or nearly so, sometimes with a small nipple at the apex, thin shelled, with the surface glossy. Inside with a larval cell held in position by thread-like white filaments. When dry the gall becomes yellowish brown, often with darker brown patches. It is then very thin shelled and brittle. Diameter 25 to 35 mm.

Externally the gall may be mistaken for that of Amphibolips confluens, but it is as a rule smaller and the larval cell is held in position by radiating fibers while the galls of confluens are filled completely with a dense spongy substance. The adults emerge in June and early in July.

Habitat: Canada; New England and Middle States; MD, VA, NC, OH, MI, IN, IO

Amphibolips inanis

Empty oak apple. 

This is a spherical gall with thin walls from which many fibers extend towards the center, these holding in place the cell in which the larva develops. The gall is between 15 and 30 mm in diameter, light yellow-green changing to light brown. Common on leaves of scarlet and red oak, Quercus coccinea and rubra. Matures in June.

Insect galls of Springfield, Massachusetts, and vicinity

Amphibolips inanis

Oak apples, i.e. galls with a central, hard kernel or larval cell, a firm (often hard) outer shell, and a spongy or fibrous intervening substance, The substance lying between the rind and the kernel is fibrous and often very scanty; Size large, kernel central, leaf usually aborted

Globose, bright green, becoming yellowish brown, slightly nippled, thin-shelled glossy leaf gall, the central larval cell supported by radiating fibers, diameter 25 to 35 mm, on Q coccinea, rubra in May and June.

Amphibolips inanis

The "empty oak apple" has been collected at the following localities: IL, IN, WI, MO, OK, MD, VA, MA, NY, and Ontario.

The galls are 18-32 mm in diameter, light green with irregularly scattered purplish spots, wall thin and somewhat translucent, produced singly on under side of leaf. At Evanston [IL] adults issued in various seasons on June 11; June 25, and July 6; at Ottawa July 8; in mountains of Virginia on July 9. 

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

Amphibolips inanis

Larger Empty Oak Apple. Green with scattered purplish spots, 18-32 mm in diameter, produced singly on under side of the leaf of Q rubra. Adults emerged June 11, June 25, and July 6 in different seasons.

Cynipid Galls of the Chicago Area

Amphibolips inanis

Quercus rubra
Leaf galls, detachable
Empty Oak Apple. Produced singly on under side of leaf, 18-32 mm in dia, light green, spotted. June.

[Photo caption]
On Q rubra. Empty Oak Apple. Adults emerged June 25 (IL); June 1-15 (DC); June 12, 21, 29 (CT); all out by July 1 (Toronto)

According to genetic results in the Ward et al 2022 phylogeny, [Amphibolips cookii](https://www.gallformers.org/gall/1143) is likely the alternate generation of the same species that induces [Amphibolips quercusinanis](https://www.gallformers.org/gall/582). In the table where this speculation is listed, A cookii is labelled as a sexual generation and A quercusinanis as an agamic gall, but this is contradicted by prior literature and may be a mistake.

Amphibolips quercusinanis is a common and distinctive gall found throughout the range of Quercus rubra. It is most commonly confused with Amphibolips confluenta/quercusspongifica, which is larger, more frequently aborts its host leaf, and tends to lack spots and have a bumpier, thicker shell. However, these characters can be misleading, and the most decisive way to tell the species apart is by comparing the internal structure. Amphibolips quercusinanis has an empty interior full of smooth, radiating strings, where confluenta has an interior either densely packed with spongy material or at least with spongy fibers. The presence of spots is especially misleading toward the southern edge of its range, where confluenta is apparently more likely to have spots and quercusinanis is less likely to occur at all. 

It can also be confused with Amphibolips quercusostensackeni, especially early in the spring, which has a similarly thin shell and empty interior with smooth fibers, but which lacks spots, remains much smaller throughout the season, and does not distort the host leaf. 

In the fall, Amphibolips cookii is often mistaken for quercusinanis. Both galls have spots and lack a spongy interior, but can be distinguished by their placement (cookii is found on buds, not leaves), their appearance (cookii has thicker, more succulent walls and fibers), and most easily by their season of appearance (cookii in the fall, quercusinanis in the spring).

In some parts of its range, Amphibolips quercusinanis co-occurs with Atrusca quercuscentricola, an oak apple of similar size, pattern, and structure found on Quercus stellata.  Aside from its host, which is often not apparent if the gall is found on the ground, Atrusca quercuscentricola has a more yellow-orange appearance and red spots, light pubescence, and occurs in the fall. It is common in Arkansas and Missouri, where Amphibolips quercusinanis is found but relatively rare. 

The gall of this species has [at least once](https://www.inaturalist.org/observations/82541020) been found on the flower stalk rather than the leaf.

Gallformers ID Notes