Agriculture Reference
In-Depth Information
there are up to six generations annually. Psylla pyri is
of no pest status in the British Isles.
ticular problem on Brussels sprout. Under dry
conditions, heavy infestations reduce the vigour
of young plants and may cause plants to wilt.
Infestations are often first noticed when, on dis-
turbing the plants during the spring, summer or
autumn, clouds of adults rise into the air; the
adults may even become active, and attract at-
tention, on sunny yet frosty days in mid-winter.
Family TRIOZIDAE
Trioza apicalis Forster
Carrot sucker
This psyllid is widely distributed in central and
northern Europe, where it is a local and usually
minor pest of carrot. Heavy infestations cause
distortion of the foliage. The insect is also associ-
ated with other umbelliferous plants, including
Anthriscus sylvestris, Heradeum sphondylium
and Pastinaca sativa. In the British Isles, carrot
sucker is restricted mainly to wild hosts in south-
ern England and is of no pest status.
BIOLOGY
Breeding commences in the spring, and females
then deposit small semicircular groups of eggs on
the underside of leaves of host plants. The eggs
hatch in 1-2 weeks. At first, the young nymphs
wander over the leaf surface but they soon settle
down to feed. Individuals are fully grown in
about 10 days. They then pupate and adults ap-
pear a few days later. There are four or more
overlapping generations annually, with adults
and some pseudo-pupae overwintering.
BIOLOGY
Adults overwinter in the shelter of spruce trees
and other conifers. In the spring, they migrate to
umbelliferous hosts where eggs are eventually
laid. The eggs hatch about 10 days later. Nymphs
feed on the leaves during the summer and pass
through five instars before attaining the adult
stage, usually in September. There is just one
generation annually.
DESCRIPTION
Adult 1.4-1.6 mm long, mainly yellow, coated
with white, mealy wax; head and thorax
marked with brown; forewings white, each with
two grey spots. Egg 0.25 mm long, whitish,
oval. Nymph flat, scale-like; mainly white, with
a pair of yellow spots; eyes red. Pseudo-pupae
pale yellow, flat and scale-like, with a waxen
fringe; eyes red.
DESCRIPTION
Adult 3 mm long, mainly green or yellowish-
green, the body of older individuals is sometimes
marked with pale brown; antennae black-tipped;
forewings 2.0-2.4 mm long, hyaline.
Bemisia tabad (Gennadius)
Tobacco whitefly
In recent years, this tropical pest has occurred in
glasshouses in both England and continental
Europe, usually having been introduced on im-
ported poinsettia plants or cuttings. In Northern
Europe, it is most likely to occur on glasshouse
ornamentals and on protected vegetable crops
such as sweet pepper and tomato. Infested tissue
becomes slightly spotted. Host plants are also
contaminated by masses of sticky honeydew and
sooty moulds.
Family ALEYRODIDAE (whiteflies)
Aleyrodes proletella (L.)
Cabbage whitefly
Cabbage whitefly is a widespread and locally
abundant pest, especially in southern areas. In-
festations occur mainly on cultivated brassicas,
including Brussels sprout, cabbage (especially
savoy cabbage) and cauliflower, but are usually
of only minor importance. The underside of in-
fested leaves becomes marked by patches of
white, mealy wax (Plate If); plants are also con-
taminated by honeydew and sooty moulds, a par-
BIOLOGY
Under favourable glasshouse conditions this
polyphagous whitefly is capable of breeding
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