Biology Reference
In-Depth Information
999
1000
999 Aruncus sawfly (
Nematus spiraeae
).
1000
Larva of aruncus sawfly (
Nematus spiraeae
).
Nematus spiraeae
Zaddach (
999-1000
)
Aruncus sawfly
A common and destructive pest of goat's beard (
Aruncus
dioicus
). Widely distributed in central and northern
Europe; in Britain, first recorded in 1924 and now often
an abundant garden pest.
Nematus tibialis
Newman (
1001-1003
)
False acacia sawfly
A minor pest of false acacia (
Robinia pseudoacacia
).
Widely distributed in mainland Europe and in England,
having been introduced from North America along with
its foodplant in the early nineteenth century.
DESCRIPTION
Adult:
5-6 mm long; yellowish brown, darker above
and with head, thorax and antennae brownish black;
tegulae pale; wings clear with brown veins.
Egg:
1mm
long; whitish and capsule-shaped.
Larva:
up to 20 mm
long; head brownish green to brown; body green and
translucent, with short, pale hairs arising from pale,
inconspicuous verrucae.
DESCRIPTION
Adult:
6-7 mm long; yellow, marked above with black;
antennae black; legs mainly yellow, the hind tibiae and
tarsi black.
Larva:
up to 12 mm long; head brownish
green marked with black; body green and shiny.
LIFE HISTORY
Adults occur in May and June, depositing eggs in
association with the young growth of false acacia.
Following egg hatch, the young larvae feed on
expanded leaves, each forming a small hole through the
leaf blade and resting along the cut edge; later, the
larvae devour more of the tissue. Larvae are fully fed in
two or three weeks. They then enter the soil and pupate
in tough, dark brown cocoons. Adults emerge shortly
afterwards. A second generation occurs in the late
summer with, in favourable seasons, a partial third
developing in the autumn.
LIFE HISTORY
Adults of this parthenogenetic sawfly emerge in late
April or May, eventually depositing eggs on the
underside of leaves of host plants. Eggs hatch in about
a week. The larvae feed in groups on the leaves during
May and June, rapidly devouring the tissue between the
major veins. Individuals are fully grown in 4-5 weeks;
they then enter the soil to pupate in silken cocoons.
A second generation of adults appears in late July or
August, and second-brood larvae feed in August and
September; in some seasons there may be a partial third
generation. Larvae of the final brood overwinter in
silken cocoons, and pupate early in the spring.
DAMAGE
Holed or partially devoured leaves attract attention on
small ornamental trees and nursery stock but damage is
rarely of any significance.
DAMAGE
Defoliation is often extensive, the leaves of plants
becoming skeletonized with only the major veins
remaining.
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