Agriculture Reference
In-Depth Information
the evolution of resistance to many insecticides, including chlorpyrifos (see
above).
Another interesting control technique was developed for onion fly during
the 1970s (Soni and Ellis, 1990). Adult onion flies were raised in culture,
sterilized using radiation or chemicals and then released into onion crops in
large numbers to mate with - and thereby reduce the fertility of - wild
populations. Reductions in the reproductive rate of the pest resulted, and the
technique has been used commercially in The Netherlands. This 'sterile male'
technique had previously been successful in the control of other insect pests.
Other dipterous pests
Certain
Eumerus
spp., bulb flies, tunnel into allium plants and can reduce bulbs
to a rotten mass. The maggots are difficult to control when inside plants, and
infested bulbs should be destroyed. Spraying of plants and the dusting of bulbs
with insecticides are used in control.
Leaf miners,
Liriomyza
spp., are small flies that lay eggs on allium leaves in
the spring. The larvae mine through the photosynthetic tissue, and severe
infestation results in leaf collapse (see Plate 4a). The flies pupate in soil. The
flies have more generations per year the warmer the climate. In central Europe
these are a severe pest. Eleven species have been reported as damaging alliums,
with
L. nietzkei
and
L. cepae
being confined to these crops. Many insecticides are
effective for control. In the early 1990s the leaf mining fly
Napomyza
gymnostoma
emerged as a disfiguring pest of chives and leeks in Austria. It has
two generations per year, one in spring and one in autumn. A monitoring and
warning service for the pest was started in that country in 1997. It can be
controlled by organophosphorus insecticides applied when larvae are in the
upper parts of the leaves (Kahrer, 1999).
Leek moth
Acrolepiopsis assectella
, the leek moth, is a severe pest of leeks in western Europe,
also attacking onion, garlic, chives and shallots (see Plate 4b). Damage is
caused by caterpillars mining within the leaves and later in the central crown
of the plant, where they create a cavity, destroy young leaves and predispose
the plants to rotting by secondary pathogens. Leek moth attack can completely
destroy young plants and seriously downgrade the harvest quality of older
plants. The caterpillars also damage seedheads and can destroy the seed crop.
Adult moths are brownish grey, with a 17 mm wingspan. Females lay up
to 200 eggs singly or in small groups near ground level on leeks and other
alliums. The yellow-green caterpillar grows to 13 mm, and ultimately weaves
a cocoon for the red-brown pupa on dead vegetation near the host plant, or
