Biology Reference
In-Depth Information
1134
1133
1133
Fruit tree red spider mite (
Panonychus ulmi
) damage to
leaves of
Sorbus aucuparia
.
1134
Schizotetranychus schizopus
damage to leaf of
Salix
.
Panonychus ulmi
(Koch) (
1133
)
Fruit tree red spider mite
This widespread and generally common mite is an
important pest of apple and various other fruit crops in
many parts of the world; it also occurs on ornamental
trees and shrubs such as almond (
Prunus dulcis
),
Cotoneaster, crab-apple (
Malus
), flowering cherry
(
Prunus
), flowering currant (
Ribes sanguineum
),
hawthorn (
Crataegus
), Japanese quince (
Chaenomeles
japonica
) and rowan (
Sorbus aucuparia
). Eggs
overwinter on the spurs and smaller branches, and hatch
from April to mid-June. There are then several
overlapping generations throughout the summer
months. Mite numbers decline from September onwards
as breeding ceases and winter eggs are laid. Unlike
Tetranychus urticae
(p. 430) the mites do not inhabit
silken webs. However, damage caused by both species
is similar, and heavy infestations lead to significant leaf
bronzing and premature leaf fall. Adult females are
0.4 mm long and dark red, with short, pale legs. They
are most commonly found (along with adult males,
nymphs, 6-legged larvae and summer eggs) on the
underside of the leaves.
Panonychus citri
(McGregor)
Citrus red spider mite
Although found mainly on citrus, this pest also occurs
on many other hosts, including evergreen ornamentals
such as Californian bay laurel (
Umbellularia
californica
), cherry laurel (
Prunus laurocerasus
),
Elaeagnus
, Japanese holly (I
lex crenata
), Japanese yew
(
Taxus cuspidata
) and Mexican orange (
Choisya
ternata
). Widely distributed in tropical and subtropical
regions, including parts of southern Europe; sometimes
also reported in greenhouses in more northerly regions.
DESCRIPTION
Adult female:
0.5-0.6 mm long; body dark purplish red
to purplish red, and distinctly rounded, with strong setae
arising from pale tubercles.
Adult male:
similar to
female but smaller, narrower-bodied and tubercles less
noticeable.
Egg:
bright red and more or less spherical.
Larva:
dark red; 6-legged.
Nymph:
brick-red; 8-legged.
LIFE HISTORY
Eggs are laid on the leaves of host plants, each held to
the surface by several radiating strands of silk. They
hatch within 1-3 weeks, depending upon temperature.
The immature stages feed for up to 2 weeks before
moulting into adults. Breeding is continuous throughout
the year and reaches an optimum at temperatures of
about 25ºC.
Schizotetranychus schizopus
(Zacher) (
1134
)
Infestations of this widely distributed and often
common mite occur mainly on crack willow (
Salix
fragilis
), white willow (
S. alba
) and other narrow-
leaved willows. The mites feed on the underside of the
leaves, particularly along either side of the midrib,
causing the foliage to become discoloured. Damage is
often severe, affecting the growth and appearance of
plants. In exceptional circumstances, the trunks and
branches of host plants become coated in sheets of
webbing. Eggs, which are laid along the midrib, are pale
yellowish and somewhat flattened, with a dorsal stipe;
DAMAGE
The mites cause a noticeable silvering, yellowing or
speckling of infested leaves; especially under drought
conditions, they may also cause premature leaf fall.
Heavy infestations weaken host plants and, in severe
cases, young shoots may be killed.
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