Agriculture Reference
In-Depth Information
May to mid-July, along either side of the mid-rib
on the underside of the expanded leaves. Eggs
take several weeks to hatch, and juvenile mites
appear on the foliage from June onwards. Young
adult mites of both sexes occur in August and
September. After mating, the males die and the
females seek out sheltered situations on the bark
in which to hibernate. In Europe, there is just
one generation annually.
DESCRIPTION
Adult
0.3 mm long, bright red, distinctly flat-
tened;
legs
short.
Egg
0.11mm long, oval,
bright red.
ORDER ASTIGMATA
Family ACARIDAE
Rhizoglyphus callae
Oudemans;
R. robini
Claparede
Bulb mites
weeks according to temperature. A dispersal
stage, known as the hypopus, may appear in
some populations. These individuals cling onto
passing insects, such as small narcissus flies,
Eumerus
spp. (p. 177
et seq.),
and then may be
carried to other breeding sites.
Bulb mites are generally common but usually
secondary pests of bulbs, corms and tubers; hosts
include many ornamentals (e.g. freesia, gladio-
lus, hyacinth, iris, narcissus and tulip), vegetables
(e.g. beet, onion and potato) and various other
crops. The mites often invade diseased or dam-
aged tissue and, once established, can cause con-
siderable damage, especially in lifted bulbs
being stored under warm conditions; the inside
of severely infested bulbs, for example, often
turns completely black and powdery. Unlike
Rhizoglyphus callae, R. robini
(a more fre-
quently reported, slightly larger species with
shorter body hairs) tends to favour relatively
healthy hosts. Attacks can also occur in the field;
the mites may then invade the growing points, so
that emerging leaves become distorted and
sometimes develop ragged or saw-tooth edges
(the latter is also a symptom of attack by bulb
scale mite,
Steneotarsonemus laticeps,
p. 262).
DESCRIPTION
Adult
0.7 mm long, translucent-whitish, very
shiny, with brownish internal markings;
body
globular, with several long hairs extending back
beyond the tip of the hysterosoma;
legs
reddish-
brown, short and stumpy.
Egg
0.2 x 0.1mm,
hyaline-whitish, smooth and shiny.
Hypopus
0.3 mm long, dark brown;
legs
short, robust and
each terminating in a large claw.
Tyrophagus longior
(Gervais)
Grainstack mite
This widely distributed pest, sometimes known
as French 'fly', is often abundant in straw and
undecomposed horse manure; infestations fre-
quently develop on cucumber plants grown on
straw bales or raised by traditional manure cul-
ture. The mites are also associated with various
stored products and may occur as secondary
invaders on bulbs and corms that have gone
mouldy during storage. When swarming upon
cucumber plants, the mites produce minute holes
in the young leaves; they also cause shoot distor-
tion and, sometimes, blindness.
BIOLOGY
Bulb mites are associated mainly with stored
crops or stored crop products, especially where
conditions are damp or mouldy. Their develop-
ment is favoured by warmth and high humidity,
and the mites will breed continuously and multi-
ply rapidly whilst conditions remain suitable.
Development from egg through a larval and two
nymphal stages to adulthood takes from 1 to 4
BIOLOGY
The mites breed continuously under favourable
conditions and the life-cycle (from egg through
