Agriculture Reference
In-Depth Information
eventually moult into new adults and these
emerge in the following spring.
Thrips tabaci
Lindeman
Onion thrips
This often abundant pest occurs on many culti-
vated plants, including leek, onion and various
glasshouse-grown vegetables and ornamentals;
the thrips are directly harmful and often cause
extensive silvering of affected tissue. Outdoor
attacks are especially severe in hot, dry weather.
Although formerly considered an important
vector of plant viruses, this no longer appears to
be so.
Cucumber and tomato:
infested foliage
and fruits become mottled, and young cucumber
leaves may develop noticeable window-like
patches; the thrips can also transmit spotted-wilt
virus.
Leek and onion:
infested foliage turns sil-
very, and leaves may subsequently twist and curl.
DESCRIPTION
Adult
1.2-1.7 mm long, dark brown;
legs
pale;
wings
greyish;
antennae
8-segmented.
Nymph
whitish to yellowish-white;
eyes
dark red.
Thrips angusticeps
Uzel
Field thrips
The field thrips is a widespread and locally
common pest of various agricultural and horti-
cultural crops, including field bean, linseed, pea,
red beet and sunflower. Infested leaves are often
discoloured and distorted. On pea crops, which
are particularly susceptible, most damage occurs
in April or May before seedlings are 5-10 cm
high; plants then become stunted and the leaves
puckered and blotched with yellow (cf. damage
caused by pea thrips,
Kakothrips pisivorus,
p.
91). Infestations are especially common follow-
ing brassica seed crops that have been infested
during the previous season.
BIOLOGY
This thrips is parthenogenetic. Eggs, usually
about 30 per female, are laid in plant tissue and
hatch within 1-2 weeks. Nymphs feed on host
plants for up to 2 weeks and then enter the soil to
complete their development. New adults appear
about a week later. Large populations may de-
velop on glasshouse-grown plants, and breeding
is continuous so long as conditions remain fa-
vourable. Outdoors, females usually overwinter
in the soil and two or more generations of adult
females and nymphs occur from May onwards.
BIOLOGY
Adult thrips with reduced wings (i.e. brachy-
pterous adults) overwinter in the soil. They
emerge in the early spring and then invade vari-
ous hosts. A generation of nymphs develops on
the young leaves and within the growing points
of the plants, which eventually gives rise to fully
winged (macropterous) adults; these migrate in
late May or early June to summer hosts, includ-
ing various brassicaceous plants (Brassicaceae).
Nymphs produced on these hosts develop into
the overwintering generation of brachypterous
adults.
DESCRIPTION
Adult female
1.0-1.3 mm long, greyish-yellow to
brown;
forewings
pale brownish-yellow, with line
of setae along vein I incomplete;
antennae
7-
segmented, yellowish-brown (cf. western
flower thrips,
Frankliniella occidentalis,
p.
91).
Egg
whitish and elliptical.
Nymph
whit-
ish to pale yellowish-orange;
eyes
red.
DESCRIPTION
Adult
1.0-1.3 mm long, mainly brown or
dark brown;
antennae
7-segmented, with a
pale third segment;
legs
mainly brown with
yellow tarsi;
forewings
with a complete row of
setae along vein II and an incomplete row
of setae along vein I.
Nymph
translucent-
whitish.
Thrips simplex
(Morison)
Gladiolus thrips
This species, which was introduced into Europe
from Southern Africa, is an important pest of
glasshouse-grown gladioli. The thrips infest the
corms and, later, cause a streaking of the devel-
