Biology Reference
In-Depth Information
Arge pagana (Panzer) ( 936-937)
syn. A. stephensii (Leach)
Variable rose sawfly
A locally common and important pest of rose ( Rosa ).
Eurasiatic. Present throughout much of mainland
Europe; in Britain most abundant in southern, south-
eastern and south-western England.
LIFE HISTORY
Adults emerge in late May or June and may then be
found on or near rose bushes. Eggs are deposited in
double rows along the young vegetative shoots or
flower stalks, the female penetrating the tissue with her
short, stubby ovipositor to form distinctive oviposition
scars; up to 20 eggs are inserted into each affected
shoot. The eggs hatch a few weeks later. The larvae then
attack the expanded foliage. At first they graze on the
lower epidermis; later, they bite completely through the
leaf tissue, either in the middle or at the edge. Fully fed
larvae drop to the ground and eventually pupate in
brown, double-walled cocoons formed in the soil. There
is often just one generation annually but, if conditions
are favourable, a second brood of larvae occurs in the
autumn.
DESCRIPTION
Adult: 7-9 mm long; head, thorax and legs mainly black;
abdomen mainly yellow; wings blackish. Larva: up to
25 mm long; head black or orange; body bluish green,
suffused above with yellowish green; body bearing
numerous, usually very prominent, black verrucae; these
verrucae form three distinct transverse rows per segment
but with just one transverse row on the last (cf. Arge
ochropus ); anal plate black; five pairs of abdominal
prolegs (cf. Arge nigripes ).
DAMAGE
Shoots containing oviposition scars become blackened
and distorted, and heavy attacks affect growth and
flowering. Larvae cause extensive defoliation, commonly
skeletonizing the leaves.
LIFE HISTORY
Adults occur from May to October, depositing eggs
in the young shoots as described under Arge ochropus .
The larvae feed voraciously from June onwards, there
being two main broods annually. When fully grown, the
larvae enter the soil to pupate in brown, double-walled
cocoons.
DAMAGE
Leaf skeletonization is often extensive, seriously
affecting shoot growth and spoiling the appearance of
bushes.
936
937
936 Variable rose sawfly ( Arge pagana ).
937 Larva of variable rose sawfly ( Arge pagana ).
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