OF EPPING FOREST.
have often found Andricus fecundatrix galls rendered polythalamous
by a number of contained Synergid larvae. Some galls, such as
Andricus collaris, which naturally fall to the ground during late
autumn, will remain on the tree when attacked by parasites.
The common oak Marble-gall (Cynips kollari) may often be
seen of smaller size and darker colour than is normally the case.
On cutting through one of these galls it will be noticed that
instead of there being one cell onlv in the centre of the gall, there
is a ring of cells present. These have been formed by Synergid
larvae and they will be found to have filled up and eliminated
the cell of the original gall-maker.
Cynips kollari galls often have knobs or excrescences upon
their surface which are caused by inquiline larvae living in the
gall substance. Biorhiza terminalis galls (the common "Oak
Apple") are particularly liable to parasitic infestation and are
inhabited by a great number of insects. As many as seventy-
five species have been collected from these galls, besides Acarina
and Araneida.
Although some changes in the appearance of a gall, such as
those mentioned with regard to Cynips kollari, are due to parasitic
infestation, they are for the most part probably caused by some
substance secreted in the salivary glands of the larva, which acts
upon the surrounding tissue, on the juices of which the larva
feeds. This would account for the remarkable variety in form,
etc., shown by the spangle-galls of the genus Neuroterus, since
the method and time of ovipositing are in each case apparently
the same.
Oviposition and growth of the Gall.
The piercing apparatus of a gall-fly is, as one would expect
to find it, of somewhat exceptional construction, the act of
oviposition being of extreme importance with these insects.
The ovipositor and its attachments take up practically the whole
of the interior of the abdomen when in repose.
The plates mentioned below are paired and the whole
apparatus is worked by five muscies.
It is made up of :—An anterior plate, a posterior plate and
a triangular plate.
The anterior plate (Fig. 4, d) is attached to the lower end
of the triangular plate (c) and the base of the posterior plate (c).