Agriculture Reference
In-Depth Information
upper surface of the foliage; the underside of
these galls appears shiny and pale green (rather
than the normal dull whitish-grey), owing to
destruction of the leaf hairs. The mites may
also cause the death of apical buds, so that weak
lateral shoots are produced; mites can also in-
vade the fruits, again destroying patches of hairs
and also causing uneven ripening and malforma-
tion. Damage is usually most severe under hot,
dry conditions and in sheltered situations;
Mailing Jewel is a particularly susceptible
cultivar. On blackberry, heavy infestations may
result in the appearance of mildew-like leaf
blotches but this host is rarely affected to any
significant degree (cf. blackberry mite,
Acalitus
essigi,
p. 256).
mites attack the growing points and recently
emerged young growth, and cause considerable
distortion, stunting and discoloration of leaves
and flowers; affected tissue often appears shiny
and may also become brittle. Heavily infested
plants can be killed.
Phytonemus pallidus
ssp.
asteris
(Karl) damages aster (especially
Aster
novi-belgii),
the flower heads on heavily infested
plants being replaced by stunted rosettes of small
leaves.
Phytonemus pallidus
ssp.
fragariae
(see p.
261) is a pest of outdoor strawberry.
BIOLOGY
The mites breed continuously under glasshouse
conditions, so long as conditions remain favour-
able, and pass through several overlapping gen-
erations each year. In unheated glasshouses,
however, breeding ceases during the winter. De-
velopment includes an egg, a larval and a quies-
cent nymphal stage. The nymphs do not feed and
are enclosed within the bloated, cast-off skin of
the larva. Females at this transitional resting
stage are often carried around by adult males,
the male holding a female nymph aloft with the
aid of a genital sucker. Tarsonemid mites are
light-shy and relatively inactive. They often shel-
ter within folded or crinkled young tissue and
between bud scales, where they also feed and
breed. Development from egg to adult takes
about 2 weeks during the summer but is much
slower when temperatures are low, duration of
the egg stage then becoming especially pro-
tracted. The mites rarely, if ever, move over
glasshouse staging or soil but adults will transfer
from plant to plant where adjacent leaves or
shoots are touching.
BIOLOGY
Adult female mites overwinter in the shelter of
the buds. They emerge at bud burst and then
migrate to the underside of the expanding leaves
to feed. Individuals may also become active at
any stage during the winter if temperatures ex-
ceed 11°C. In spring, eggs are deposited amongst
the leaf hairs, where colonies of mites then de-
velop; there are several overlapping generations
throughout the season. Populations on the fruit-
ing canes reach their peak from mid-summer
onwards. Mites sometimes occur on the flowers
and developing fruits. Infestations also spread to
the new vegetative growth, especially as leaves
on the fruiting canes harden and become less
suitable as feeding sites.
DESCRIPTION
Adult female
0.f2mm long, pale yellow and
elongate (overwintering form darker in colour);
prodorsal shield setae
of medium length.
DESCRIPTION
Adult female
0.25 mm long, elongate-oval, some-
what barrel-shaped, pale brown, shiny and
translucent;
hindlegs
narrow, each ending in a
whip-like seta;
gnathosoma
longer than broad
(cf. bulb scale mite,
Steneotarsonemus laticeps,
p.
262).
Adult male
smaller than female;
body
with a genital sucker;
hindlegs
stout, each with a
characteristic inner flange and a strong claw (see
Fig. 171) (cf. broad mite,
Polyphagotarsonemus
latus,
p. 261).
Egg
0.12mm long, elliptical, whit-
Family TARSONEMIDAE
(tarsonemid mites)
Phytonemus pallidus
(Banks)
Cyclamen mite
This widely distributed mite is a major pest of
glasshouse ornamentals, including African vio-
let, begonia, cyclamen, ivy and many others. The
