Agriculture Reference
In-Depth Information
pest in continental Europe. Unlike
Hoplocampa
testudinea
(p. 250), males are fare and reproduc-
tion is mainly parthenogenetic; otherwise, the
biology of both species (apart from choice of
host plant) is very similar.
Hoplocampa flava
(L.)
Plum sawfly
Infestation of this local species occur on damson
and plum. Losses on garden and orchard trees
can be considerable but attacks tend to be spo-
radic and unpredictable. The mainly brownish to
orange-coloured adults (3.5-5.5 mm long) occur
in April, and eggs are then deposited singly in the
fruitlets of host plants. The creamish-white
larvae feed within the fruitlets. They produce
masses of wet, black frass (cf. fruitlet-mining
tortrix moth,
Pammene rhediella,
p. 222). Fully
grown larvae enter the soil and form cocoons, in
which they eventually overwinter. In common
with related species, there is just one generation
annually.
Fig. 335
Young larva of apple sawfly,
Hoplocampa
testudinea
(x20): (a) tip of abdomen (further
enlarged).
about 2-3 weeks, the larva vacates the original
fruitlet and invades an adjacent one, usually en-
tering directly through the skin on the basal half;
further fruitlets may be attacked before larvae
are fully grown and drop to the ground. Larvae
overwinter in the soil in silken cocoons, formed
several centimetres (and often as deep as 25 cm)
below the surface. Pupation occurs in the spring,
a few weeks before the emergence of the adults;
some larvae, however, may remain in the soil for
one or more seasons before attaining the adult
stage.
Nematus ribesii
(Scopoli)
Common gooseberry sawfly
This generally abundant sawfly is a notorious
pest of gooseberry; infestations also occur on, for
example, red currant and white currant, but not
on black currant (cf.
Nematus olfaciens,
p. 252).
Two- or three-year-old bushes are most likely to
be attacked. Initial infestations tend to occur on
the central, lower parts of bushes but they soon
spread upwards and outwards. The larvae feed
gregariously and rapidly defoliate the branches
to leave only a skeletal framework of major
veins. Heavy infestations cause considerable loss
of plant vigour and cropping potential is
reduced.
DESCRIPTION
Adult
6-7 mm long, shiny black dorsally and or-
ange ventrally;
wings
more or less clear, with
brown veins.
Egg
0.8 mm long, white and trans-
lucent, elongated and slightly curved.
Larva
up
to 12 mm long;
body
whitish;
head
yellowish-
brown;
abdominal prolegs
seven pairs present;
caudal plates
(on abdominal segments 8-10)
inconspicuous.
Young larva
whitish;
caudal
plates
on abdominal segments 9 and 10 very con-
spicuous
(Fig. 335)
but the plate on abdominal
segment 8 small and inconspicuous
(Fig. 335a);
head
blackish.
BIOLOGY
Adults occur from April or May onwards. Eggs
are eventually laid in rows in slits made in the
major veins on the underside of the leaves of
host plants. The eggs hatch about 8-10 days later.
Larvae then feed ravenously. They pass through
Hoplocampa brevis
(Klug)
Pear sawfly
This species is associated with pear and, although
local and uncommon in England, is an important
