Agriculture Reference
In-Depth Information
continuously, but development from egg to adult
tends to be slower than that of the glasshouse
whitefly, Trialeurodes vaporariorum (below).
Eggs are deposited singly, usually low down on
the underside of the young leaves. On hatching,
the first-instar nymphs wander for a short dis-
tance before becoming sedentary and beginning
to feed; they pass through three instars before
moulting to a non-feeding pseudo-pupal stage.
Unlike T. vaporariorum, the eggs and scales
are scattered on the leaves, rather than clumped
together.
favourable, each female being capable of depos-
iting 200 or more eggs over a 6-week period;
reproduction is normally parthenogenetic. At
normal glasshouse temperatures, eggs hatch in
about a week to 9 days. The nymphs (the so-
called 'scales') at first wander over the foliage
but soon become sedentary on the underside of
the leaves, where they continue their develop-
ment. They pass through three instars before
entering a brief, non-feeding, pseudo-pupal
stage. Development from egg to adult usually
takes less than a month and populations in
glasshouses can build up very rapidly, with a
succession of overlapping generations occurring
throughout the summer.
DESCRIPTION
Adult 1mm long, mainly white; when at rest,
wings held in a relatively steep, roof-like posture
(cf. Trialeurodes vaporariorum, below). Egg
0.2 mm long, pear-shaped, whitish when newly
laid but later becoming brownish. Nymph flat,
scale-like, mainly yellowish. Pseudo-pupa
0.7 mm long, slightly pointed posteriorly; unlike
that of T. vaporariorum lacking waxen processes.
DESCRIPTION
Adult 1mm long, pale yellow to whitish;
wings white, and held relatively flat when in
repose (cf. tobacco whitefly, Bemisia tabaci,
above). Egg 0.2mm long, yellowish, broadly
conical, becoming blackish after a few days.
Nymph translucent to pale green, oval, flat,
scale-like. Pseudo-pupa oval, whitish, 7 with
relatively short marginal waxen processes and
several pairs of long waxen tubes dorsally.
Trialeurodes vaporariorum (Westwood)
Glasshouse whitefly
Family APHIDIDAE (aphids)
The glasshouse whitefly is a major pest of pro-
tected crops, occurring on aubergine, cucumber,
climbing French bean, melon, sweet pepper, to-
mato and various ornamentals. Whilst conditions
remain favourable, the insects may also survive
on various weeds out of doors. Infested plants
show poor growth and the foliage may become
discoloured; when attacks are heavy, leaves wilt
and die, and crop yields will be depressed. At-
tacked plants become coated in honeydew, upon
which sooty moulds soon develop; vegetables
such as cucumbers and tomatoes often need to
be washed before they can be marketed.
Acyrthosiphon pisum (Harris)
Pea aphid
This species is a widespread and common pest of
culinary pea (Plate 2a) and certain other culti-
vated legumes, including field bean and sweet
pea; the aphid is also a virus vector. Most dam-
age is caused to the growing points during June
and July, with leaves and pods becoming dis-
torted and turning yellow; heavy infestations on
culinary peas will reduce yields significantly. Pea
enation mosaic virus, pea leaf roll virus and pea
mosaic virus are introduced and spread by this
insect.
BIOLOGY
Whitefly infestations occur mainly on the under-
side of leaves, eggs being typically deposited
in circular groups on smooth leaves but more
scattered on hairy ones. Adults are particularly
abundant on the uppermost parts of plants, and
readily take to the wing when disturbed. They
breed continuously whilst conditions remain
BIOLOGY
Adults and eggs overwinter on perennial leg-
umes such as clover, lucerne and trefoils. Colo-
7 Pseudo-pupae parasitized by the glasshouse whitefly
parasitoid (Encarsia formosa Gahan) are black.
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