Agriculture Reference
In-Depth Information
Fig. 333
Larva of hazel sawfly,
Croesus
septentrionalis
(x4).
attention; damage, however, is of little or no
importance.
Fig. 334
Adult
Dolerus puncticollis
(x3.5).
BIOLOGY
Adults occur mainly from May to June. Eggs are
deposited in the edges of expanded leaves; each
egg enlarges before hatching to produce a promi-
nent swelling in the leaf lamina. Larvae are most
numerous in June and July. They feed on the leaf
tissue for 4-6 weeks before becoming fully
fed. They then moult into active prepupae and
enter the soil, where they eventually pupate but
without forming cocoons (cf.
Pachynematus
clitellatus,
p. 252). There is one generation each
year.
Hoplocampa testudinea
(Klug)
Apple sawfly
This sawfly is an important pest of apple. The
larvae burrow singly within the developing
fruitlets and produce masses of wet. black frass;
this is exuded through a small hole (c. 1.5 mm in
diameter) in the side of each infested fruitlet (cf.
damage caused by codling moth,
Cydia
pomonella,
p. 218, and fruitlet-mining tortrix
moth.
Pammene rhediella,
p. 222). Attacked
fruitlets remain small, are often deformed and
are noticeably pubescent. They usually drop pre-
maturely and crop losses can be considerable,
particularly on susceptible dessert cultivars such
as James Grieve and Worcester Pearmain. At-
tacked fruitlets sometimes bear long slit-like
wounds that arise from the calyx; these indicate
that the larva has failed to penetrate into the
flesh. Such fruitlets often develop to maturity,
with characteristic, corky, ribbon-like scars.
DESCRIPTION
Adult
9-10 mm long, mainly metallic black
with a green and bluish sheen;
pronotum and
tegulae
red (in female).
Larva
up to 18 mm
long;
body
greenish-white to creamish-white,
but blackish dorsally, with a black mark
over each thoracic leg;
head
marked with black;
abdominal prolegs
eight pairs present
(Plate
16d).
BIOLOGY
Adults occur during April and May. They are
active during sunny weather, especially around
mid-day. After mating, eggs (typically about 30
per female) are laid singly in the apple blossom,
each inserted in a slit made immediately below
the sepals by the female's saw-like ovipositor.
Eggs hatch in about 2 weeks. Each larva then
penetrates into the receptacle of the fruitlet to
feed on the flesh; they also enter the ovary and
attack the developing pips (seeds). Infested
fruitlets usually fail to develop further. After
Dolerus puncticollis
Thomson
This generally common and widely distributed
species is also a minor pest of cereals. The adults
(9-10mm long)
(Fig. 334)
are mainly black, with
the apex of each femora and the base of each
tibia reddish. They occur from late April or early
May onwards and may often be seen flying
around the periphery of cereal fields. The larvae
feed on the foliage of cereals during the summer
months and, eventually, pupate in the soil. There
is one generation each year.
