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THE OAK GALLS AND GALL INSECTS
becoming purple when older, due to a rind which covers the
galls. This peels off later, leaving the gall beneath brown and
striated. Shape; That part of the gall visible through the split
bark is conical in shape. The larval chamber is in the lower,
deeply imbedded part, which is dilated.
Imago.
Colour: reddish-brown. Antennae: dark brown, paler at the base. Thorax:
median segment and basal scutellar sutures dark. Abdomen: reddish brown, 3rd
segment finely punctured. Legs; reddish brown.
(11.) Sexual Generation. Ia. Andricus testaceipes (Htg.)
Inquiline. Synergus apicalis (Htg.)
Gall.
A thickening of the leaf stalk or vein of the leaf contains the
gall lying within in a hollow chamber. I have found two
specimens in the shoot, which I at first mistook for A. trilineatus
(Htg.) galls. Colour: Yellowish green.
Imago.
Colour: black. Antennae: Dark. Basal joints paler. Thorax: May be
slightly hairy at the base of mesonotum. Abdomen: orange, darker above. Legs:
orange yellow, the base of hind coxae brownish.
Account of Generation Cycle.
If the galls of A. sieboldii, when mature, are kept through the
winter, the insects emerge in April or May. The buds are pricked
by them near the base, as in A. radicis (Fab). The resulting gall in
some cases resembles A. trilineatus, but the eggs are deposited in the
rudimentary leaves, the gall appearing usually in the veins and
petiole of the leaf. The flies from this gall emerge in August,
Oviposition takes place through the bark of young stems near the
ground, the eggs being laid as a rule in a ring. The bark begins
to swell in the autumn, but ceases to do so during the winter.
During May in the following spring the red conical galls appear,
the reddish rind covering the galls breaks off, and they mature in
June, but the flies do not emerge till the following April or
May.
OCCURRENCE IN EPPING FOREST.
Andricus sieboldii. Uncommon. I only met with a few
specimens of this gall growing from the stems of some old
pollard oaks. The galls, which were situated near the bases of
the stems, were old and dried up.