Acraspis erinacei (sexgen)

Acraspis erinacei (agamic)

Dryophanta erinacei (Mayr)

[of the agamic gall:] It is widely distributed, having been reported from New England, North Carolina, Iowa, Illinois, Indiana, Kansas, Michigan, Ohio, Virginia, Canada, and probably Florida and Colorado. 

The [agamic] insect makes its way to the leaf and flower buds of the white oak, where oviposition takes place. On the tree where our observations were made, it continued to emerge and oviposit until the twenty-first of November. 

Buds were examined on the eighth of May and the unhatched eggs found were very turgid, appearing slightly enlarged. On the twelfth of May a slight swelling, at the apex of which an empty egg shell was visible, appeared on the lower green portion of the scale, (Fig. 9, Pl II). This proved to be a freshly formed gall, containing a young larva of Dryophanta erinacei. The gall at this stage was thin-walled, with a pebbled surface, greenish in color, and contained a watery fluid. The egg-shell remains attached to the apex of the gall until the latter has reached considerable size, when it dries up and disappears. These hypertrophies develop rapidly, as many as three appearing on one scale. The wall of the gall has by this time changed to a yellowish brown color, and soon becomes quite dry and brittle. 

Galls also develop on the apical portion of the leaf and flower buds, (Fig. 10, Pl II). These are red, being similar in color to the young leaf and flower. The wall is pebbled on the surface, and thin. The cavity contains a single larva bathed in a watery fluid, and similar in all respects to the one inhabiting the scale gall. The terminal galls are of the same size as those on the scales, varying in number from one to four, and when mature are reddish brown. Since only the agamic form of Dryophanta erinacei was found ovipositing on the leaf and flower buds, and since the eggs of this species and no other were found in the leaf and flower region, and since males and females similar in size and character emerge from the two galls, it is evident that they are produced by the same insect. The difference in color in the galls is due to the normal difference of the tissue of which they are formed. 

Shoots were brought into the laboratory, placed in water and covered with bell jars. Here about noon on the twenty- first of May the first male and female emerged. They were quite vigorous, and about four-thirty in the afternoon the female was noticed actively moving along the midrib of the young leaf. Suddenly she stopped, and set up a rapid nodding motion which lasted thirty-five seconds, during which the ovipositor was thrust into the tissue. The insect remained motionless for a time, then withdrew the ovipositor, filling the passage with a yellow substance which, as in the agamic form, is probably a secretion poured forth by the accessory glands of the reproductive system. The process was repeated four times in succession without moving the body forward. Each time the ovipositor was inserted the body was curved slightly more than at the preceding puncture. The entire time occupied by the four ovipositions was from four-thirty- four to four-fifty, or sixteen minutes, thus allowing four minutes to each oviposition of which a little over two minutes and a half was occupied by the passage of the egg. Many other observations were made, and the time in all instances corresponded to the first recorded.

In the open the adults did not emerge until the twenty-ninth of May, and continued to oviposit from that time until the fifth of June. 

Dryophanta erinacei (Mayr)

The Oak Hedgehog Gall is rounded or oblong, with the surface finely netted with fissures, and more or less densely covered with spines. It varies in length from 10-15 mm, and occurs on both sides of the White Oak leaf. The point of attachment is generally on the midrib (Fig. I, Pl I), though it is often found on the lateral veins. When young it is yellowish green, but in autumn it becomes yellowish brown, much lighter in color than the tinting of the leaf. The gall first appears late in June, and reaches full development about the third week in August. It is widely distributed, having been reported from New England, North Carolina, Iowa, Illinois, Indiana, Kansas, Michigan, Ohio, Virginia, Canada, and probably Florida and Colorado. 

A longitudinal section through the gall shows that it contains several chambers varying from two to eight in number. These I have named according to their location. First to be noted are the central cavities, (Fig. 2a, PI. I), which measure 2 mm x 3 mm and are located in the central portion of the growth. These are occupied by Dryophanta erinacei and the parasites. Second, there are the lateral cavities, (Fig. 2b, Pl I), situated at the side and base of the growth and measuring 13 mm x 2 mm. These are occupied by inquilines. Lastly, there are to be found the peripheral cavities, (Fig. 8a, Pl II), located on the coriaceous portion of the gall, and covered with the basal layer of spines. These are 1 mm in size, and are likewise occupied by inquilines.

The gall was first described by Walsh in 1864 under the name Cynips q. erinacei. When Mayr in 1881 established the genus Acraspis he included the insect causing this gall, which therefore was known as Acraspis erinacei. The first description of the insect appeared in a paper by Beutenmiiller '09, entitled "Species of Biorhiza, Philonix, and their allied Genera, and their Galls," in which he places it in the genus Philonix. As will be shown later in this discussion, the insect belongs to the genus Dryophanta, and should be known therefore as Dryophanta erinacei (Mayr).

The Life-History of Dryophanta Erinacei. 

In the open the [sexgen] adults did not emerge until the twenty-ninth of May, and continued to oviposit from that time until the fifth of June. The egg is oval, provided with a pedicel 750m. in length. It is always placed in the fibro-vascular bundles, and at an angle of about 80° to the axis of the leaf.

On the twenty-fifth of June the first evidences of gall-formation appeared on the leaf-veins, the hypertrophied tissue pushing through the slightly ruptured epidermis. In galls gathered on the first and second of July, larva were found measuring 375 um. During the summer, molts were observed after which the larva measured 750 um, 1.25 mm, 1.75 mm, 2.25 mm, respectively, thus showing five stages during the life-history. Fig. 19, PI. Ill, shows a larva 1.75 mm, obtained about the middle of August. From this time, the thorax does not show a great increase in size,, but the abdomen loses its reflexed character, becomes globose,, and increases in size until pupation. The first pupa was obtained on the fifth of September, but the adults did not emerge until the fifth of November. Fig. 5, PI. I, shows a pupa of the agamic form. 

The agamic form of Dryophanta erinacei emerges from the oak hedgehog gall about the fifth of November. 

The insect makes its way to the leaf and flower buds of the white oak, where oviposition takes place. On the tree where our observations were made, it continued to emerge and oviposit until the twenty-first of November. The insects are most active on cold days or early in the morning. During the warm weather they are inactive and sluggish, hiding at the base of the petioles, in the crotches of the young shoots, or in the crevices of the bark. They have been taken in this vicinity on rare occasions in early December, but usually they succumb to the first heavy frosts at the close of November.

A Study of Dryophanta Erinacei (Mayr) and Its Gall