Agriculture Reference
In-Depth Information
to the effects of drought. The mites do not pro-
duce webbing.
BIOLOGY
Eggs are laid during the summer on stones, clods
of soil and other non-plant surfaces, usually in
the vicinity of host plants. Diapausing eggs
remain
in situ
for extended periods during hot,
dry conditions before hatching. Non-diapausing
eggs, however, hatch in approximately 1-2
weeks, and the initially bright red immature
stages feed for a similar period before becoming
adults. This species is parthenogenetic and
motile stages occur throughout the year.
Fig.
344
Female fruit tree red spider mite,
Panonychus ulmi
(x80).
DESCRIPTION
Adult female
brown and broadly pear-shaped,
tapering posteriorly;
legs
very long, especially
the first pair, and relatively narrow;
body setae
simple (cf. clover bryobia mite,
Bryobia
praetiosa,
p. 265).
Egg
more or less spherical
and shiny, either white (a diapausing egg) or
bright red (a non-diapausing egg); the latter has
a distinctly ribbed cap.
tree conditions become unsuitable for further
breeding; this often occurs when mite numbers
are large and foliage becomes badly bronzed.
DESCRIPTION
Adult female
0.4 mm long, oval, strongly convex,
dark red;
hysterosomal setae
relatively long and
arising from conspicuous white tubercles;
legs
pale
(Fig. 344). Adult male
smaller than female
and pear-shaped, tapering posteriorly; yellowish-
green to bright red.
Egg
red and shiny; more or
less spherical (c. 0.1mm in diameter) but slightly
flattened and the top drawn into a fine stipe.
Active immature stages
pale yellowish-green to
bright red.
Tetranychus urticae
Koch
Two-spotted spider mite
Infestations of this generally abundant mite
occur on a wide range of plants, including glass-
house ornamentals (e.g. carnation, chrysanthe-
mum and rose) and vegetables (e.g. cucumber,
sweet pepper and tomato), indoor and outdoor
fruit crops (especially wall-trained fruit trees,
bush fruits, cane fruits and strawberry) and hops.
Serious attacks may also occur on hardy
ornamentals and outdoor vegetable crops (in-
cluding French bean and runner bean), espe-
cially in hot, dry summers; occasionally,
infestations also develop on potato and sugar
beet. The mites feed mainly on the underside of
leaves; they withdraw sap from the plant cells
and this leads to a pale spotting of leaves and,
later, distinct speckling, silvering or bronzing;
infested parts of plants may also become coated
in webbing. Heavy infestations often lead to
withering of leaves and premature leaf-fall; on
Petrobia latens
(Miiller)
Stone mite
This widespread but minor pest is associated
mainly with members of the Poaceae and, if nu-
merous, will cause damage to various crops, in-
cluding carrot, lettuce and onion. Symptoms
range from a yellow speckling of leaves to a gen-
eral bronzing; also, the foliage often becomes
shrivelled and brittle. Attacks, which tend to de-
velop in patches, are most often noted under dry
conditions; the symptoms caused appear similar
