Agriculture Reference
In-Depth Information
posteriorly.
Nymph
yellow when young, later
becoming orange;
abdomen
with a dark brown
tip in the second instar.
DESCRIPTION
Adult female
1.6-1.8mm long, black to
brownish-black, with fully developed wings;
head
as large as pronotum (prothorax);
antennae
8-segmented;
pronotum
transversely rectan-
gular;
legs
yellowish.
Adult male
similar to
female but smaller and apterous.
Egg
0.3 mm long, whitish-yellow.
Nymph
whitish or
yellowish.
Pupa
whitish to pale yellow;
eyes
reddish.
Limothrips cerealium
Haliday
Grain thrips
This thrips is generally abundant on cereals (es-
pecially wheat and oats) and grasses, and often
causes concern. Developing grains of heavily in-
fested florets become shrivelled and discoloured;
infested florets may also become blind. Germi-
nation of seed is affected adversely and, on bar-
ley, attacks can result in poor malting quality of
the grain. Damage caused to crops, however, is
rarely extensive and the pest is usually of only
minor significance. Mass nights of adult females
in summer (these are the familiar 'thunderflies')
often constitute a nuisance, especially when
the insects invade glasshouses, homes, gardens
and amenity areas. The thrips readily gain entry
through seemingly impenetrable joints or cracks,
and are often then implicated in the triggering of
burglar-, fire- and smoke-alarms. In continen-
tal Europe, infestations of
Limothrips
on cereal
crops often occur in association with
Haplothrips
aculeatus
(p. 94), an uncommon species in the
British Isles.
Limothrips denticornis
Haliday
Barley thrips
This often common and widely distributed
species is also associated with various species
of Poaceae, especially barley and oats. Adults
are most readily distinguished from those of
Limothrips cerealium
(above) by the asymmetri-
cal third antennal segment, which is drawn out-
wards into a distinct, thumb-like prominence.
Taeniothrips inconsequens
(Uzel)
Pear thrips
Infestations of this often common thrips occur
on various deciduous trees, especially pear but
also apple and plum. The thrips feed within the
flower buds; sap often seeps from the damaged
tissue. Later, they attack the petals, stamens and
styles of open flowers, to produce brownish
patches and distortion; young leaves are also at-
tacked. Heavy infestations lead to reduced fruit
set and to russeting of fruitlets.
BIOLOGY
Adult females overwinter away from host plants,
often sheltering beneath the bark of conifer
trees. They become active from late May on-
wards and migrate to host plants where eggs are
laid, each placed in a small slit cut into the plant
tissue. The eggs hatch within 2 weeks. The
nymphs then feed within the shelter of leaf folds,
beneath leaf sheath, or in the developing flowers,
and pass through two instars. They are fully
grown in about 2 weeks and then enter brief
propupal and pupal stages (within the ear or a
leaf sheath) before the appearance of the new
adults. Mating takes place before the short-lived
males die. The females then migrate in vast
masses, at about harvest time, before taking up
their winter quarters. There is typically one gen-
eration annually.
BIOLOGY
Adults of this mainly parthenogenetic,
univoltine thrips appear from January or
February onwards. They then feed in the swell-
ing and opening buds of host trees. Eggs are laid
during May, either in leaf veins or in the blossom
stalks (pedicels), and they hatch about 10 days
later. The nymphs feed for several weeks and
eventually, when fully grown, enter the soil.
Each forms a small earthen cell within which the
propupal and pupal stages occur. Individuals
