172 THE OAK GALLS AND GALL INSECTS
When they occur in great numbers on a single plant, as is
often the case with young stock, they are exceedingly injurious.
I have seen many young trees covered with the galls, completely
stunted and practically useless.
The galls are of little or no use for ink making purposes,
because as Cameron remarks, they contain only seventeen per
cent. of tannic acid as against fifty per cent. in Aleppo and other
galls.
The presence of tannic acid in the gall acts perhaps as a
protection for the enclosed larva, though birds often peck the
galls open to get at the grub, in spite of their bitter properties.
The galls are very liable to parasitic infestation and harbour
inquilines and commensals; the presence of these intruders can
often be told by various wart-like excrescences which appear on
the outer surface of the galls.
(27). Agamic. I. Cynips kollari (Htg.)
Inquilines. Synergus pallicornis, S. melanopus (Htg.) and S.
reinhardi (Mayr).
Gall.
Appears from terminal and axillary buds. Round in shape,
varying in size up to 3 mm. Green to brownish red when
young often at this time marked with darker spots, the apex is
usually drawn out and slightly bent. As they become older and
grow larger they assume a golden yellow colour or remain quite
green; in both cases they turn brown subsequently, at
maturity.
Single celled unless parasitised.
Very often two galls may be found joined in one, in which
case there is usually one larval cell containing a single larva.
The gall substance is much harder immediately around the
larval chamber than elsewhere, with the exception of the outer
epidermal tissue of the gall.
Imago.
Colour: Reddish yellow, which varies slightly in intensity. Antennae:
13-jointed, basal joint pale, third joint longer than the others. Thorax:
Pubescent, parapsidal furrows complete, scutellum completely covers the
metanotum which, like the median segment, is very dark. Abdomen: Smooth,
shining, more or less black above, partially covered with a silky pubescense.
Ovipositor: Long and spiral. Legs: Yellow, paler than the body, fore tibrae
fringed with hairs. Wings: Long, hyaline, and slightly hairy.