154 THE OAK GALLS AND GALL INSECTS
bark of stems or trunk. I have found the insects during early
spring in a mature condition in the galls.
OCCURRENCE IN EPPING FOREST.
Andricus corticis. Very common, especially in the callus
formed by the exposed cambium where the bark of old trees has
split down. On account of their brown covering, these galls are
easily passed over, but after the insects have emerged they
present a very typical appearance, having a punctured rim
showing where the vascular bundles have passed through to
nourish the upper part of the gall.
I have taken mature flies from these galls in February.
Andricus gemmatus. Common. First appearance noted,
June 20th.
I have sometimes found these galls on the leaf petiole.
(13.) Agamic Generation. III. Andricus radicis (Fab.)
Inquiline. Synergus incrassatus (Htg.)
Gall.
Appears on the root of the oak, sometimes on the trunk of
the tree partly above ground. Galls which appear on the roots
may also be often exposed. Colour: White and soft at first,
varying with increasing age from yellowish pink to bright red,
becoming brown and woody later.
Shape and size differ considerably; four or five galls often ap-
pear in one mass, though each gall can easily be separated. In
some cases the galls greatly resemble potatoes, but usually they
present a cracked and wrinkled appearance. Larval cells
numerous.
Imago
Colour: Reddish brown. Abdomen: Red. Antennae; Colour varies.
Basal 4-5 joints brownish red; apex darker. Thorax and head: Pubescent.
Mesonotum with a large central and two lateral dark lines. A dark transverse-
line in front of the scutellum. Metathorax dark. Abdomen may have a dark
blotch on the first segment. Legs: Reddish, base of coxae black, tibiae and
claws infuscated. Wings Hyaline, a few hairs sometimes present.
(13.) Sexual Generation. IIIa. Andricus trilineatus
(Htg.)
Inquilines. Synergus apicalis, S. vulgaris (Htg.), Ceroptres arator
(Htg.)