Agriculture Reference
In-Depth Information
oping leaves and flower stems. Direct damage
to flowers results in silver flecking; affected
tissue eventually turns brown. Breeding is con-
tinuous under suitable conditions (temperatures
above 10°C) and, on outdoor-planted hosts, is
favoured by hot, dry conditions. Adult thrips
are 1.5 mm long and dark brown, with 8-
segmented antennae; the nymphs are yellowish
or orange.
developing ears. The eggs hatch about 10 days
later. Nymphs then feed for 3-4 weeks, each
passing through two instars. At first, the nymphs
feed within the developing flowers but, later,
they attack the outer surface of the developing
grain. When fully grown, usually in early July,
the nymphs emerge from the ears and drop to
the ground. They then burrow into the soil to
aestivate, typically at a depth of about 30cm. In
early October, the nymphs reappear and then
overwinter under dry grass and straw. Pupation
occurs from mid-March onwards. There is just
one generation annually.
Family PHLAEOTHRIPIDAE
Haplothrips tritici
(Kurdjumov)
Wheat thrips
DESCRIPTION
Adult
1.5 mm long and mainly black;
antennae
black and 8-segmented;
abdomen
with last seg-
ment tube-like (see Fig. 47b).
Egg
0.3mm long,
elliptical and translucent.
Nymph
mainly bright
red;
head, antennae, legs and tip of abdomen
black.
This thrips is associated with grasses and cereals,
especially wheat. On bread-making wheats, di-
rect feeding on the ovaries leads to considerable
distortion of developing grain, some of which
may abort; infestations may have an adverse
effect on yield and can also lower the baking
quality of the harvested grain. On hard wheats,
infestations often lead to considerable discolora-
tion of the grain. Although an important pest in
continental Europe, this thrips is not found in the
British Isles.
Haplothrips aculeatus
(F.)
This widely distributed thrips occurs on various
kinds of Poaceae and related families (e.g.
Juncaceae). In continental Europe (but not in
the British Isles, where it is uncommon), it is a
potentially important pest of grasses and occurs
in considerable numbers on all the main culti-
vated species.
BIOLOGY
Adults appear in the early spring and later fly
into wheat fields. Females eventually crawl into
the sheaths of wheat plants to deposit eggs in the
ORDER TRICHOPTERA (CADDIS FLIES)
Family LIMNEPHILIDAE
Limnephilus lunatus
Curtis
November. Jelly-like batches of eggs are laid in
the autumn on the leaves and stems of watercress
plants, each placed a few centimetres above the
surface of the water. The newly laid egg batch
soon swells, following the absorption of water,
to become a colourless, gelatinous mass up to
10 mm in diameter, in which the individual eggs
(of which there may be several hundred) are
arranged in distinct rows. The eggs hatch in
about 3 weeks; however, development of the
embryos may be delayed if the water tempera-
ture drops below 10°C. The case-inhabiting lar-
vae feed for several months and pass through five
This caddis fly is a frequent pest of watercress.
The larvae feed on the leaves, roots and stems,
and often cause considerable damage. Infesta-
tions in watercress beds are especially harmful
during the winter months, when pieces of plant
severed by the larvae float away and are lost.
BIOLOGY
Adults appear from late May or June onwards,
with some individuals surviving well into
