170 THE OAK GALLS AND GALL INSECTS
gradually getting rid of wings which are of no service to them
and are even a hindrance when laying their eggs in the roots of
the tree.
(26).—Agamic Generation. I. Trigonaspis renum (Htg.)
Inquilina Synergus thaumacera (Dal.)
Gall.
The galls are situated on the back of the leaf, usually there
are a great number on each leaf. They are small irregular galls
very often kidney-shaped, but the form varies. Greenish white
to red in colour, becoming brown later, when mature, unless
parasitised. They are arranged along the leaf veins.
Imago.
Colour; Brownish to yellowish red. Antennae: Thirteen-jointed. Thorax:
Punctured, dull; scutellum: hairy. Abdomen: Shining, vertex shagreened;
almost sessile. Legs: Lighter yellow than the body; claws: simple. Wings:
None.
(26.)—Sexual generation. Ia. Trigonaspis crustalis
(Htg.)
Inquilines. Synergus thaumacera (Dal.) S. facialis and S.
pallicornis (Htg.)
Gall.
Appears from adventitious buds near the base of the oak
trunk, on shoots growing from the trunk, or on shoots growing
out of the ground from acorns dropped from the trees. Shape:
Globular, size variable. Apex sometimes pointed. Colour:
White, yellowish white, pink, or bright red.
Imago.
Colour: Black (abdomen, red), shining. Antennae: Dull reddish brown at the
base, darker towards apex. Thorax: Black. Head: Black. Abdomen: Red
or bright orange, shining, distinctly pedunculate. Legs: Orange, base of coxae
infuscated. Wings: Long and well developed, clouded in front of the cubitus
and often at the base of the radial cellule.
Account of the Generation Cycle.
The flies from the Trigonaspis renum galls appear in December
and January, though sometimes later. The eggs are laid in the
adventitious buds on the tree trunks, or on buds on young stems.
In April the small red gall of Trigonaspis crustalis appears, but in
cases where oviposition has taken place later, these galls do not
form until as late as the middle of May. From the end of May
until the middle of June the flies emerge, the females pricking