Cynips minuta

Cynipidae

Neuroterus

Quercus alba

Alabama

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Quercus bicolor

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Quercus montana

Cynipid galls of the eastern United States

The Gall Wasp Genus Neuroterus

Neuroterus minutus (sexgen)

Cynips minuta, n. sp.

As soon as the leaves of Quercus alba begin to expand in the spring, a few buds are occasionally seen that develop into a cluster of greatly enlarged petioles without a leaf blade, or at most only a very rudimentary one. They are three or four times the size of those of a full grown leaf, and each contains a number of larvae of the small gall insect which I have named C minuta. The larvae mature very rapidly and the imagos leave the gall about the time that the leaves are full grown. Occasionally an embryo leaf seems to have escaped the sting of the mother insect, and a fully developed leaf appears among the galls, but such instances are not common. The galls are pubescent and usually of a pinkish color. The insects are of both sexes.

New Cynipidae (1881)

Neuroterus (Dolichostrophus) minutus bisexual forms

GALL. — An inseparable swelling, varying greatly, depending upon the part of the plant affected; on Quercus alba, Q. bicolor, and probably related white oaks. 

RANGE. — Connecticut to Pennsylvania. Probably thruout eastern North America. 

This species is the eastern equivalent of Neuroterus quercicola, differing mainly in having a lighter color, the abdomxen not produced, and the first abscissa slightly arcuate. The galls of variety minutus resemble leaf galls of quercicola. Neuroterus irregularis is closely related to minutus, but the males of the two are very distinct. The two varieties of minutus have what might appear to be radically different galls, but several similar cases of gall polymorphism are recorded in this paper for this genus. The galls of variety pallidus are "monothalamous" clustered, seed- like, anther galls; those of minutus are irregular, polythalamous, petiole or vein swellings. The diversity is probably the result of the relatively simple gall-producing physiologies of the insects and of the differences of the affected plant tissues. A consideration of gall polymorphism, and of the nature of anther galls, will be found in the introduction to this paper. That one of the varieties should be known only from the leaf galls on Q. alba, the other only from the ament galls on Q. bicolor may evidence merely our lack of sufficient data. Both galls may be found on both oaks, but if this is not shown, then an examination of the vernations of the buds in which the insects oviposit may explain the matter. There is little chance of there being any great differences in the physiologies of the two varieties. Each of the two described varieties is confined, it would appear, to a single species of oak. About 40 varieties should occur on related oaks in the eastern half of North America. The bisexual insect is short-lived, its gall evanescent, and consequently not often collected. An alternate, agamic generation, producing perhaps a stem or leaf swelling, probably exists, but I fail to recognize this form among any of our described species of Neuroterus, 

Neuroterus minutus variety minutus

GALL. — An elongate, irregularly cylindrical swelling of a petiole or midvein. Polythalamous, with a moderate number of cells. Each gall irregularly cylindrical, elongate, up to 5. mm. in length, sometimes several galls more or less fused; covered with normal tissue and an additional pubescence, pinkish when young, drying brownish. Internally more or less solid, with the larval cells rather closely packed, without distinct cell walls. On petioles and leaf veins, more or less dwarfing and deforming the leaf; on Quercus alba (figs. 45, 46). 

RANGE. — Connecticut: Waterbury (Bassett). New York, New Jersey, Pennsylvania (Beutenmuller). Probably confined to Q, alba in a northeastern part of the US.

Bassett described this gall as appearing as soon as the oak leaves begin to expand, in April or May, and maturing within a few weeks, by the time the leaves are fully expanded. The above descriptions are made from a good-sized series of types. 

Neuroterus minutus

The galls of this species have been taken at Winnetka, Ravinia, and Moline, IL.; at Plummer Island and Takoma Park, Md.; at Washington, D. C; at Falls Church and Alexandria, Va.; and at Fairfax, S. C. In the Chicago area the galls are rare and contained pupae one year on May 30 and the next year on June 9. Adults were all out at Moline by June 19. About Washington the galls are very abundant especially in 1924 when two large white oaks had almost every twig end affected. The galls contained pupae on May 4 and adults emerged May 6-12, males appearing first. Galls collected at Falls Church :May 2, 1920, gave adults :May 7. Brodie found galls at Toronto. 

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

Neuroterus minutus 

Quercus alba, prinus [montana]
Bud galls
Cells in greatly enlarged petioles without a leaf blade, puberulent, often pinkish, in early spring.

[Photo caption]
On Q alba. Also on Q prinus. Adults of both sexes out May 7-10 (DC). Galls on Q alba were bagged on May 6. No result visible when the bag was taken off on June 13. In July there were hundreds of translucent spots on the leaves. 