OAK GALLS IN EPPING FOREST
35
holes by which the flies had emerged. Galls of occultus occur
at or near the top of the catkins, and have the effect of restricting
their development, so that they may be half the usual length or
very much shorter; indeed they are sometimes so abbreviated
that the galls are more or less hidden amongst the scales of the
opening bud; hence the name given to the fly from a character
of the gall. Closer search discovered a few galls without holes,
and also galls of Neuroterus aprilinus Giraud from which the flies
had gone, of Neuroterus quercus baccarum L. in the young stage,
one gall of Andricus albopunctatus Schlechtendal, several young
galls of Biorhiza pallida Olivier (the oak-apple gall) and what I
hoped were galls of Andricus callidoma Hartig form cirratus Adler,
the presence of the last galls being indicated by long white hairs.
On 24th and 26th April more sprays were collected, but by
the last date someone had removed the greater part of the bough.
Later more twigs bearing catkins were found on the ground and
were searched for cirratus galls, some well developed and typical
galls of the form being collected from a near-by tree. Examina-
tion of the sprays produced 316 occultus galls having emergence
holes, and from other galls 38 flies of the form were bred.
The cirratus galls first found were less closely placed than is
usual, and the development of some of them probably ceased
when the bough and twigs were broken off. There were
apparently many galls, and although about 40 flies were bred,
this in my opinion was a relatively small yield from the probable
number of galls. Close examination of the flies proved beyond
question that they were the form cirratus. Previously I had not
bred either occultus or cirratus flies from Epping Forest galls.
A spray of oak gathered near Broadstrood by a member of the
party on the Club's excursion on 27th April bore occultus galls,
but holes in the galls showed that the flies had gone. These
flies seem to leave the galls almost as soon as the galls are
noticeable; this is also true of N. aprilinus, but I think that the
search of a tree heavily laden with young catkins may reward the
optimist, if not with occultus galls, with those of some other
species almost as elusive. When the catkins have begun to die,
examination of those still having green stalks may result in small
galls being found.
This year I have again bred flies of Andricus foecundatrix
Hartig form pilosus Adler from galls collected near Chingford;
this is another small gall, bearing fewer and shorter hairs than
the cirratus gall, and occurring on catkins. Two galls of Andricus
circularis Mayr, collected from a tree of Quercus cerris L. near
Baldwin's Pond on the Club's excursion already mentioned,
yielded two male flies.
May 31st, 1946.