Agriculture Reference
In-Depth Information
trees. Heavy infestations are particularly damag-
ing at the pre-blossom stage, when the nymphs
cause the petals of the opening buds to turn
brown; this often leads to the death of blossom
trusses. These symptoms are often mistaken for
frost damage. Nymphal attacks on foliage are of
little significance; feeding by adults also appears
to be of no economic importance.
and fruits are contaminated by honeydew, ex-
creted in profusion by the nymphs, and by sooty
moulds that subsequently develop on the honey-
dew; affected fruits may be unmarketable unless
washed or wiped clean.
BIOLOGY
Unlike apple sucker, this species is multivoltine
and overwinters in the adult stage. The adults are
active in sunny weather, even in mid-winter.
They invade pear orchards from February on-
wards, eggs then being deposited on shoots and
spurs. The eggs hatch in late March and April.
First-instar nymphs invade the opening buds and
blossom trusses; they then begin to feed. There
are usually three generations each year and pest
numbers typically increase at each generation
and reach a peak in the late summer. Summer
eggs are usually deposited on the underside of
fully expanded leaves, often clustered in large
numbers along the mid-rib. In autumn, adults of
the final generation fly away from pear trees to
seek overwintering sites in nearby hedges and
other shelter.
BIOLOGY
This pest overwinters as eggs on the fruit spurs of
host plants, laid usually along the leaf scars; they
may also occur on the shoots and around the base
of leaf buds. The eggs hatch in the spring, usually
during April. The nymphs soon gain access to
the buds, as these begin to open. The nymphs
develop through five instars and, although attack-
ing leaves, are most numerous in blossom trusses.
They excrete globules of honeydew and also pro-
duce white, waxen threads, which often highlight
the presence of the pest. Nymphs are fully fed in
late May or early June. The new adults remain
active on host trees throughout the summer, and
fly readily when disturbed; mating, followed by
egg laying, occurs in August and September, and
may also extend into the autumn. There is just one
generation annually.
DESCRIPTION
Adult
1.5-2.0mm long, brownish-black to
reddish-brown;
wings
transparent
(Fig. 187);
winter form
darker, with cloudy patches on the
wings.
Egg
0.3 mm long, elongate-oval and
lemon-yellow to orange;
pedicel
moderately
long.
Nymph
pinkish to orange, with dark
brown to blackish markings; older individuals,
and nymphs of the first generation, tend to be
darkest.
NOTE In parts of continental Europe,
Psylla pyri
(L.)
is the main psyllid pest of pear; its biology is similar to
that of
P. pyricola,
with adults overwintering, but
DESCRIPTION
Adult
2.5-3.0mm long, mainly apple green,
yellowish-green or brownish-yellow;
wings
transparent.
Egg
0.4 mm long, elongate-oval,
pale yellow.
Nymph
flat, oval-bodied, yellow-
ish or pale brown (when young) to bright green;
eyes
red and conspicuous;
wing buds
very notice-
able in older individuals.
Psylla pyricola
Forster
Pear sucker
This psyllid is an important pest of pear, and
heavy infestations often result in fruit distortion
and premature leaf-fall; summer infestations
may have a deleterious effect on fruit-bud devel-
opment and can check tree growth. Nymphs of
the first generation can also cause direct damage
to blossoms, the petals turning brown. Foliage
Fig. 187
Pear sucker,
Psylla pyricola
(x25).
