Agriculture Reference
In-Depth Information
short stalk. Puparium yellowish-brown; ante-
rior spiracles borne on a pair of prominent, di-
verging stalks.
Phytomyza syngenesiae (Hardy)
larva = A chrysanthemum leaf miner
Infestations of this leaf miner (widely known in
older literature as 'Phytomyza atricornis , \ see
also under P. horticola, p. 193) are often estab-
lished on various members of the Asteraceae,
especially glasshouse crops such as chrysanthe-
mum; severe infestations are also reported on
lettuce. The whitish to brownish larval mines are
disfiguring and, if several occur on the same leaf,
infested leaves may wilt, turn brown and die.
Adult leaf-feeding punctures, which sometimes
develop from small, whitish spots to brownish
warts, are also disfiguring. Although usually re-
garded as a pest, the insect has been tested in
New Zealand as a potential biological control
agent for use against the weed Senecio jacobaea.
Phytomyza rufipes Meigen
larva = Cabbage leaf miner
This generally abundant species is a minor pest
of brassica crops, including broccoli, cauliflower,
mustard and oilseed rape. Attacked seedlings
may become malformed, especially if the larval
mines extend into the stems, but damage caused
to established plants is usually of little or no
significance. Infestations on autumn-sprouting
broccoli (= calabrese) can be troublesome, and
the presence of larvae in crops sent for process-
ing sometimes leads to the rejection of consign-
ments. In the autumn, the pest is sometimes
abundant on oilseed rape, but the larvae tend to
occur in the senescing outer leaves and damage
caused is unimportant.
BIOLOGY
Adult females deposit eggs singly through punc-
tures made in the upper surface of leaves. The
eggs hatch a few days later. The larvae then mine
within the leaves to form long, winding, narrow,
wavy-edged (cf. American serpentine leaf miner,
Liriomyza trifolii, p. 189) galleries, clearly visible
from above. Black pellets of frass are deposited
irregularly to one side along the length of the
mine. Larvae as usually fully fed after 7-10 days.
Each then burrows to the lower surface of the
leaf to pupate in a small chamber, with the an-
terior spiracles of the puparium protruding
through the lower epidermis (cf. Phytomyza
horticola, p. 193, and Liriomyza trifolii, p. 189).
Adult flies emerge one or more weeks later. The
duration of the various stages depends on tem-
perature, and breeding in glasshouses is continu-
ous if conditions remain favourable, e.g. where
all-year-round (AYR) chrysanthemums are
grown. On outdoor hosts, there are usually two
generations annually.
BIOLOGY
Adults occur from May or June to September.
Eggs are laid in leaves of suitable hosts, each
placed close to a major vein. Larvae commence
feeding by burrowing into nearby veins that they
then follow into the mid-rib. Most feeding occurs
within the mid-rib or petiole with, often, several
larvae attacking the same leaf. Larvae in young
plants may also enter the stem. Pupation usually
occurs in the soil and adults appear approxi-
mately 6-8 weeks after eggs were laid. There are
two generations annually and, under favourable
conditions, a partial third.
DESCRIPTION
Adult mainly grey with sides of thorax yellow;
wings 2.5-3.5 mm long. Larva up to 6 mm
long, shiny white and maggot-like (Plate 8d);
mouth-hooks set more or less at right-angles
to rest of mouthparts; anterior spiracles short
but prominent and many-lobed; posterior
spiracles with up to 30 minute pores and directed
more or less downwards (cf. Scaptomyza flava,
p. 185). Puparium 3 mm long, pale brownish-
yellow.
DESCRIPTION
Adult greyish-black, faintly marked with pale
yellow on the head and sides; legs mainly black,
with pale yellow knees; wings 2.2-2.6 mm
long. Larva up to 3.5 mm long, greenish-white;
mouth-hooks set more or less at right-angles to
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