OF EPPING FOREST.
155
Gall.
Found in shoots of one year's growth, giving in some cases an
uneven appearance; in others their presence is only noticeable
after the insects have emerged by the small round holes in the
shoots.
Imago.
Very variable. Colour: Brownish-red. Antennae; Dark. Legs: Testaceous,
hind coxae dark. Wings: Hyaline. Thorax- and Head marked with, or almost
entirely, black. Abdomen: Dark. The male differs from above in being more
shining and having the legs of a dusky orange colour, the coxae, hind tibiae and
femora darker. Head, thorax, and abdomen usually quite black.
Account of Generation Cycle.
The asexual flies emerge from the A, radicis galls usually in
April or May; and after resting, deposit their eggs in the base of
the buds, the resulting galls appearing in the twig. Sometimes
I have found the flies ovipositing as late as the middle of June,
when the bud has partially developed. In either case the galls
formed are A. trilineatus. When oviposition takes place as late as
June, the galls are easily recognisable, as the eggs are crowded
into one shoot, causing it to swell considerably. The sexual
flies emerge from these galls, and oviposit in the roots in August,
many eggs being laid together. The gall (A. radicis) breaks
through the swollen root in September, but in October gall
growth ceases until the following spring. The flies then mature in
autumn, and emerge in the spring of the year following, usually in
April or May.
OCCURRENCE IN EPPING FOREST.
Andricus radicis. Abundant. I found these galls either
singly or 5 or 6 together; in the latter case they appear to form
one gall on the root, but on removal they fall apart. They may
appear quite above ground, be partially covered with earth or
be entirely beneath the soil. They do not always appear on the
root, but may grow direct from the trunk, either just above or
below the ground. I have sometimes found these galls on the
roots of young oak plants grown scarcely a foot high. The
insects from the A. trilineatus galls seem to prefer ovipositing at
some place on the root where an A. radicis gall has previously
grown, so that old dried-up and woody galls of A. radicis may
often be found near the fresh specimens.