OF EPPING FOREST.
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galls appear in May, maturing at the end of the month. During
June the sexual generation of flies emerges, oviposition taking
place on the root (sometimes, according to Adler, in the leaf bud).
The females may be apterous, but the males are always winged.
OCCURRENCE IN EPPING FOREST.
Biorhiza aptera. Fairly plentiful and probably abundant,
but less noticeable on account of their situation.
Biorhiza terminalis. Very abundant. Occur singly or two or
three together, many growing from the terminal buds. They are
found also growing from the axillary buds. They vary greatly
both in size and colour, and are very subject to parasites and
commensals of almost every insect order.
Some trees were simply a mass of galls, which remain on the
tree in many cases during the greater part of the winter. First
appearance noted, May 10th.
Genus TRIGONASPIS (Hartig).
The Agamic Forms of this genus are wingless like the
corresponding forms of the genus Biorhiza, but they are all much
smaller in size; the head is also dilated behind the eyes, and the
ovipositors differ considerably. The sexual form is very well
marked and entirely different to the agamic generation, the
wings being large and well formed and the abdomen red in
colour. There is only one British species at present known.
It has not been ascertained for what reason there is an egg
resting stage in the agamic generation. The eggs are deposited
in the leaf by the sexual flies, at the end of May or beginning of
June, but the larvae do not leave the eggs, and gall growth does
not commence, until September.
The reason for the apterous condition of the agamic
generation is probably due to the fact that the perfect insects do
not require their wings before oviposition as the eggs are
deposited in the adventitious buds on the trunks of the trees,
usually near the ground, or in buds on young stems from six
inches to a foot in height, which grow up around the trees
from acorns which have fallen to the ground and germinated.
It is quite the exception to find galls at any great distance from
the ground.
The same thing applies to those Biorhiza terminalis females
which are apterous, namely, that they would appear to be