Biology Reference
In-Depth Information
Delia radicum
(Linnaeus)
syn.
D. brassicae
(Bouché);
D. brassicae
(Wiedemann)
Cabbage root fly
A notorious and generally common pest of vegetable
brassicas, but also sometimes a problem on
brassicaceous ornamentals such as
Alyssum
, stock
(
Matthiola
) and wallflower (
Cheiranthus cheiri
).
Holarctic. Present throughout Europe.
Delia platura
(
Meigen
)
syn.
D. cilicrura
(Rondani)
Bean seed fly
Although associated mainly with vegetable crops,
infestations of this world-wide pest also occur on
ornamentals such as
Anemone
,
Freesia
and hollyhock
(
Alcea rosea
); damage is also reported on conifer
seedlings. Attacked plants lack vigour and may be killed;
seedlings arising from attacked freesia corms sometimes
turn bluish. Adults are active from May onwards. Eggs
are then deposited in the soil, particularly in the presence
of decaying organic matter. They hatch within a few
days. The larvae then tunnel inside germinating bean
seeds, young stems and other suitable plant tissue. They
feed for 1-3 weeks before pupating in the surrounding
soil, each in an oval (4-5 mm long), reddish-brown
puparium. New adults appear 2-3 weeks later; after
mating, females initiate a further generation, each
depositing about 50 eggs. There are usually 3-5
generations annually. Adults (6 mm long) are greyish
brown; the larvae (up to 8 mm long) are white and
relatively robust, with distinct, curved mouth-hooks and
12 posterior tubercles. The posterior respiratory stigmata
each have 8-10 projections.
DESCRIPTION
Adult:
6-7 mm long; grey to blackish.
Egg:
1 mm long;
elongate-oval, white and ribbed longitudinally.
Larva:
up to 10 mm long; creamy white, with prominent
papillae on the anal segment.
Puparium:
6-7 mm long;
elongate-oval, reddish brown.
LIFE HISTORY
Individuals overwinter as pupae within puparia. Adults
emerge in the spring from mid-April onwards, the
precise timing of their appearance depending on
temperature. Eggs are deposited in the soil close to the
stems of host plants, the period of egg laying often
coinciding with the flowering of cow parsley
(
Anthriscus sylvestris
). Eggs hatch after 3-7 days, the
larvae immediately attacking the roots of adjacent host
plants. They feed for 3-4 weeks and then, when fully
grown, move away through the soil for a few
centimetres before pupating. Adults of the second
generation appear in late June and July, and those of the
third from mid-August onwards, the two generations
tending to overlap so that subsequent egg laying can
occur at virtually any time from July to September.
DAMAGE
Seedlings or recent transplants collapse and die, the
fibrous roots and much of the tap root being destroyed.
Older or less heavily infested plants wilt in warm, dry
weather and make poor growth; damaged root systems
are also liable to subsequent attack by fungal pathogens.
Search WWH ::
Custom Search