This species has two
sub-species: Helicoverpa armigera armigera
is native and widespread in central and southern Europe, temperate Asia and
Africa; Helicoverpa armigera conferta
is native to Australia, and Oceania.H. armigera armigera has also invaded
Brazil and afterwards spread across most of South America and the Caribbean.It is a migrant species, capable of
reaching Northern Europe..
The cotton bollworms vary both in
size and color.The body length
reaches 12 to 20 millimeters and the wingspan 30–40 millimeters.The fore wings are yellow to orange in
females and green to gray in males.The hind wings are pale yellow with a narrow brown band at the
external edge and a dark round spot in the center.
The female cotton bollworm can lay several hundred eggs on various
parts of z plant.The eggs may hatch
into larvae within three days and the whole lifecycle can be completed in
about one month.The eggs are
spherical and
0.4 to 0.6 millimetres in diameter, and have a ribbed surface.They are white, later becoming
greenish.The larvae develop over 13
to 22 days and may attain a length of
40 millimetres by the sixth instar.Their color varies, but most are greenish and yellow to dark
brown.The head is yellow with
several spots.Three dark stripes
extend along the dorsal side and one yellow light stripe is situated under
the spiracles on the lateral side.The larvae's ventralbody
parts are pale.They are quite
aggressive carnivores that sometimes become cannibalise.If disturbed, they drom from the plant and
curl up on the ground.The pupae
develop inside a silken cocoon over 10 to 15 days in soil at a depth of
4–10 centimetres or in cotton bolls or the ears of maize.
These bollworms are very polyphagous
on an array of crop hosts including tomato, cotton, pigeon pea, chickpea,
rice, sorghum, and cowpea.Other
hosts include groundnut, okra, peas, field beans, soybeans, lucerne, Phaseolus spp., other Leguminosae,
tobacco, potatoes, maize, flax, Dianthus,
Rosa, Pelargonium, Chrysanthemum, Lavandula
angustifolia, a number of fruit trees, forest trees, and a range
of vegetable crops.In Northern
Europe, the larvae attack more than 120 plant species, especially those in
the genera Solanum, Datura, Hyoscyamus,
Atriplex, and Amaranthus..However, most damage is caused to cotton, tomatoes, maize,
chick peas, alfalfa, and tobacco. The economic threshold of harmfulness in
central Asia is three to five larvae per hundred plants of long-staple cotton
and eight to 12 larvae per hundred plants on medium-staple cotton.In cotton flowers that have been attacked
may open too early and thus remain stay fruitless.Damaged bolls fall off a plant and others will fail to produce
lint or have inferior quality lint.Secondary infections by fungi and bacteria are common and can result
in rotting fruits.Injury to the
growing tips of plants may disturb their development, maturity may be
delayed, and the fruits may be dropped.Control measures include the use of an adulticide that attractsand kills the insects, growing of resistant
varieties, weeding,inter-row
cultivation,removing crop residues,
deep autumn ploughing,winter
watering to destroy the pupae,the
use of insecticides or biological control through the release of parasitoids
such as Trichogramma spp. and Habrobracon hebetor.Tracking in the field is facilitated by
the use of sex pheromone traps.Development of Bt cotton (genetically modified to produce Bacillus thuringiensis toxin) may
improve yields of lint.
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