Agriculture Reference
In-Depth Information
buds' in the early spring, from the grape growth
stage onwards; emergence is favoured by
warm, humid conditions, the mites often swarm-
ing on the outside of the galls in considerable
numbers. Individuals eventually migrate over
the bushes and are also carried from bush to
bush by insects, wind or rain. This dispersal pe-
riod lasts into the summer but is at its peak in
May, from early flowering to early fruit swelling.
New buds are invaded in June or early July,
when egg laying begins. The mites breed rapidly
within the buds from early summer onwards,
particularly as the buds begin to swell, and
populations reach their maximum in September.
Egg laying ceases temporarily in the early winter
but resumes in January; breeding activity
reaches a second peak in the early spring, when
attacks may also spread to the growing points of
apical shoots.
Epitrimerus piri
(Nalepa)
Pear rust mite
Heavy infestations of this widely distributed pest
sometimes develop on pear trees. The mites then
cause extensive bronzing of the underside of
leaves and also russeting of ripening fruits, espe-
cially around the calyx and on the cheeks. Infes-
tations also occur on
Crataegus.
BIOLOGY
This mite is free-living and deuterogenous, with
two adult female forms (protogynes and
deutogynes) (see under apple rust mite,
Aculus
schlechtendali,
p. 256). The mites occur on un-
furling leaves, blossoms and developing fruitlets
but are most numerous beneath the fully ex-
panded leaves. There are several overlapping
generations throughout the summer, and breed-
ing continues into the early autumn. Deutogynes
(= winter females) appear in increasing numbers
from July onwards; they overwinter beneath bud
scales and in other shelter, eventually reappear-
ing and depositing eggs in the spring.
DESCRIPTION
Adult mite
0.2-0.4 mm long, whitish and vermi-
form;
hysterosoma
finely cross-striated, with
equal numbers of tergites and sternites;
pro-
dorsal shield setae
absent.
NOTE
Similar-looking mites associated with other
Ribes
hosts are recognized as distinct species, e.g.
Cecidophyopsis grossulariae
Collinge on gooseberry
and
C. selachodon
Eyndhoven on red currant.
DESCRIPTION
Protogyne
0.13-0.16mm long, yellowish to
brownish-orange, fusiform and rather flattened;
hysterosoma
with numerous microtubercles and
a distinct mid-dorsal ridge;
prodorsal shield
with
an anterior lobe;
prodorsal shield setae
short and
directed inwards (cf. pear leaf blister mite,
Eriophyes pyri,
below).
Deutogyne
similar to
protogyne but smaller and the hysterosoma with-
out microtubercles.
Colomerus vitis
(Pagenstecher)
Vine leaf blister mite
Infestations of this widely distributed pest
occur on grape vines; the mites sometimes in-
duce the development of large, whitish to yellow-
ish erinea on the underside of the leaves; the
upper surface of each gall becomes reddish-
brown and blister-like (cf. leaf galls on vines
inhabited by the grape phylloxera,
Viteus
vitifoliae,
p. 123). Such damage often causes con-
siderable leaf deformation and is attributable to
the erineum strain of the mite. Two other strains
are known: a bud strain (= 'grape bud mite') and
a leaf-curling strain. Adult mites are 0.16-
0.20mm long, elongate and pale yellowish in
colour.
Eriophyes pyri
(Pagenstecher)
Pear leaf blister mite
This widely distributed gall mite is a generally
common pest of pear. The mites induce the de-
velopment of blister-like galls on the underside
of leaves, especially along either side of the mid-
vein. The often reddish-tinged galls are visible
from above as pale green to yellowish blisters,
each 2-5 mm in diameter; these may spread over
much of the leaf surface. The galls eventually
