Agriculture Reference
In-Depth Information
orange apically and marked with yellow later-
ally;
antennae
yellow basally;
legs
yellow.
Egg
1.5 mm long, yellow.
Larva
up to 25 mm long;
body
yellowish-orange with pale longitudinal
stripes, a pair of shiny black prothoracic plates
laterally, a pair of prominent antennae and
prominent anal cerci;
head
black and shiny;
tho-
racic legs
well developed;
abdominal prolegs
absent (see Fig. 145).
within which to overwinter. Pupation occurs in
the spring.
DESCRIPTION
Adult female
9-10 mm long, elongate, mainly
black and shiny, with bright yellow patches or
bands on the abdomen (especially on the fourth
and sixth segments);
antennae
black, filiform and
noticeably thickened towards the tip;
wings
hyaline, with black veins
(Fig. 329). Adult male
similar in appearance to female but marked
more extensively with yellow
(Plate 16a).
Larva
up to 12 mm long;
body
elongate and
mainly yellowish-white;
head
yellowish-brown
(Plate 16b);
anal segment
with a slightly
chitinized dorsal spine;
thorax
with three pairs of
fleshy leg-like tubercles (these are not always
obvious) but body otherwise apodous
(Fig. 330).
Family CEPHIDAE (stem sawflies)
Cephus pygmeus
(L.)
Wheat stem sawfly
This widely distributed sawfly is a pest of winter
wheat but will also attack barley, rye, other ce-
reals and grasses. Although of major importance
in many parts of its range (notably in eastern
Europe) in some areas (including the British
Isles) the insect is now less important than for-
merly; possibly, numbers declined following the
adoption of post-harvest straw burning. It re-
mains to be seen whether banning of straw burn-
ing will lead to an increase in the pest status of
this insect. Plants attacked by wheat stem sawfly
larvae are undernourished, dwarfed and weak-
ened; typically, the ears fail to develop properly
and the seed heads turn white. Such plants often
break off a few centimetres above ground level,
especially in heavy rain or in a strong wind.
BIOLOGY
Adults occur from late May or June to July. They
are often found in the vicinity of cereal fields,
where they forage for pollen on Umbelliferae
and various other plants, including late-flowering
oilseed rape. Eggs are laid singly in the stems of
cereal plants, each inserted just below the ear
through a slit formed close to the uppermost
node. The egg hatches 7-10 days later. The larva
then bores downwards within the pith and even-
tually, typically about a month later, reaches the
base of the stem. The larva then bites around the
wall of the stem to form a line of weakness, and
plugs the hollow stem below this point with a
mixture of frass and fragments of tissue removed
from the wall; the larva then spins a cocoon
Fig. 329 Female wheat stem sawfly,
Cephus pygmeus
(x4).
Fig. 330
Larva of wheat stem sawfly,
Cephus
pygmeus
(x9).
