Mites - Pests of Ornamental Trees, Shrubs and Flowers - page 402

1085 1086

1085 Cone gall of birch witches' broom mite ( Acalitus rudis ).

1086 Witches' broom galls on Betula .

BETULA

Aceria leionotus (Nalepa)
syn. Eriophyes laevis lionotus Nalepa
Birch bead-gall mite
An often common species, inhabiting small ( c . 1 mm
diameter), red, pimple-like galls on the upper side of the
leaves of birch ( Betula ). Although sometimes numerous
the galls cause little or no distortion.

Acalitus rudis (Canestrini) ( 1085-1086 )
syn. A. rudis calycophthirus (Nalepa)
Birch witches' broom mite
Abundant on birch ( Betula ), in association with various
symptoms. In some cases, buds are invaded. These then
fail to open and, instead, become greatly enlarged and
cone-like. Shoot growth on affected branches is then
disrupted but, because infestations are most frequently
established on mature trees, damage caused is
insignificant. The mites are c . 0.19 mm long, whitish
and slender-bodied, with about 65 abdominal tergites
and sternites, and a pair of backwardly directed setae
arising from tubercles close to the hind margin of the
prodorsal shield. The mites also inhabit witches' broom
galls on birch trees, and were once considered to be
their initiators; however, it is now generally accepted
that they are merely inquilines, the growths being
induced by fungi ( Taphrina spp.). Species of Taphrina
are also responsible for the development of witches'
broom galls on certain other trees. Such fungi also
induce leaf-curl galls, including the well-known peach
leaf curl (caused by T. deformans ); these galls are
sometimes mistaken for pest-induced deformities,
particularly if invertebrates (such as mites or small
insects) are sheltering within them.

Aceria longisetosus (Nalepa) ( 1087 )
syn. A. rudis longisetosus (Nalepa)
This mite inhabits whitish, often reddish-tinged erinea
on the underside of the leaves of birch ( Betula ). The
galls also develop on the upper surface of the foliage,
and are capable of causing noticeable distortion.

CARPINUS

Eriophyes macrotrichus (Nalepa) ( 1088 )
Hornbeam leaf gall mite
A southerly distributed species which induces an
interveinal furrowing on the leaves of hornbeam
( Carpinus betulus ), the affected foliage becoming
distinctly crinkled and discoloured. Although damage is
disfiguring, and sometimes appears of some
significance, plant growth is not affected. The causal
mites are c . 0.16 mm long and relatively plump.