Agriculture Reference
In-Depth Information
ated before there is any adverse effect on crop-
ping. Apple cultivars vary in their susceptibility
to this pest. In integrated pest management sys-
tems, the presence of this mite can be useful for
maintaining populations of predatory mites (e.g.
Typhlodromus pyri
Scheuten) at times when spi-
der mites (the preferred hosts) are at low levels.
Aculus fockeui
(Nalepa & Trouessart)
Plum rust mite
Recently, infestations of this generally common
pest have become more significant (at least in
some areas). The mites inhabit the underside of
expanded leaves of both fruiting and ornamental
species of
Primus,
often in considerable num-
bers. Infestations on young leaf trusses result in
the development of large spots on young green
shoots, a distinctive yellow flecking of the leaves
and, sometimes, distortion. Heavy populations
may cause severe bronzing and lead to the death
of young leaves. Along with certain other free-
living species, the mites attack both established
and young trees and are sometimes troublesome
in gardens, nurseries and orchards. Some fruiting
cultivars, especially Victoria, are particularly
susceptible.
BIOLOGY
The mites are free-living and deuterogenous,
with two adult female forms (protogynes and
deutogynes) which differ both structurally and
physiologically. Protogynes (= summer females)
and males are the primary forms; these breed
normally throughout the summer, and there are
several (often four or five) overlapping gen-
erations each year. Development from egg to
adult includes two nymphal stages and is com-
pleted in just over 2 weeks at temperatures of
16°C; the egg stage is relatively protracted.
Deutogynes (= winter females), for which there
is no equivalent male stage, appear in increasing
numbers from July onwards. They hibernate
under bud scales, and reappear early in the fol-
lowing spring. They then invade the opening
buds and eventually lay eggs that give rise to the
first generation of protogynes and males. Large
numbers of mites of all stages of development
may be found on expanded leaves throughout
the summer months but populations decline rap-
idly following the production of deutogynes and
their subsequent migration to overwintering
sites.
Cecidophyopsis ribis
(Westwood)
Black currant gall mite
This mite is an important and widely distributed
pest of black currant. The mites induce the for-
mation of characteristic 'big buds'. Also, leaves
that emerge from infested apical shoots are often
deformed and have rounded outlines to the main
lobes. Affected bushes grow vigorously but crop
poorly. 'Big buds', that may reach 15mm in di-
ameter, are particularly noticeable after leaf-fall.
They remain on bushes throughout the winter
and into the following summer, when they even-
tually dry out and die. Although having a direct
effect on host plants, black currant gall mite is
of greatest significance as a vector of reversion
virus disease. The presence of this virus is often a
major cause of the decline of bushes and it
will shorten considerably the economic life of
plantations.
DESCRIPTION
Protogyne
0.14-0.18 mm long, yellowish-
brown to dark orange-brown and fusiform;
prodorsal shield
slightly granular;
prodorsal
shield setae
long and directed backwards.
Deutogyne
similar to protogyne but prodorsal
shield not granular and prodorsal shield
setae shorter.
Adult male
0.14-0.15 mm long,
orange-yellow to dark orange brown.
Egg
0.05
x 0.03 mm, oval and translucent.
Nymph
whit-
ish to pale orange-brown;
prodorsal shield
granular.
BIOLOGY
Black currant gall mites live and breed within the
shelter of swollen, galled buds, each of which
may contain many thousands of individuals.
Adult mites begin to emerge from these 'big
