Helicoverpa armigera
Encyclopedia
The cotton bollworm, corn earworm or Old World (African) bollworm, Helicoverpa armigera, (also known as the scarce bordered straw in the UK, where it is an immigrant) is a moth
, the larvae of which feed on a wide range of plants, including many important cultivated crops. It is a major pest in cotton and one of the most polyphagous and cosmopolitan
pest species. It should not be confused with the similarly named related species Helicoverpa zea
.
The cotton bollworm is very variable in both size and colour. The body length varies between twelve and twenty milimetres with a wingspan of thirty to forty milimetres. The forewings are yellowish to orange in females and greenish-gray in males, with a slightly darker transversal band in the distal third. The external transversal and submarginal lines and the reniform spot are diffused. The hind wings are a pale yellow with a narrow brown band at the external edge and a dark round spot in the middle.
The eggs
are spherical, 0.4 to 0.6 milimetres in diameter and have a costate surface. They are white, later becoming greenish.
The larvae
take thirteen to twenty two days to develop, reaching up to forty milimetres long in the sixth instar
. Their colouring is variable but mostly greenish and yellow to red-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 ventral parts of the larvae are pale. They are rather aggressive, occasionally carnivorous and may even cannibalise each other. If disturbed they fall from the plant and curl up on the ground.
The pupae develop inside a silken cocoon
over ten to fifteen days in soil at a depth of four to ten centimetres, or in cotton bolls or maize ears.
, 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 twelve larvae per hundred plants on medium-staple cotton. In cotton crops, blooms that have been attacked may open prematurely and stay fruitless. When the bolls are damaged, some will fall off and others will fail to produce lint or produce lint of an inferior quality. Secondary infections by fungi and bacteria are common and may lead to rotting of 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 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 entomophages such as Trichogramma
spp. and Habrobracon hebetor. Monitoring is possible by the use of sex pheromone
traps.
Moth
A moth is an insect closely related to the butterfly, both being of the order Lepidoptera. Moths form the majority of this order; there are thought to be 150,000 to 250,000 different species of moth , with thousands of species yet to be described...
, the larvae of which feed on a wide range of plants, including many important cultivated crops. It is a major pest in cotton and one of the most polyphagous and cosmopolitan
Cosmopolitan distribution
In biogeography, a taxon is said to have a cosmopolitan distribution if its range extends across all or most of the world in appropriate habitats. For instance, the killer whale has a cosmopolitan distribution, extending over most of the world's oceans. Other examples include humans, the lichen...
pest species. It should not be confused with the similarly named related species Helicoverpa zea
Helicoverpa zea
The larva of the moth Helicoverpa zea is a major agricultural pest. It can feed on many different plants during the larval stage. Accordingly, the species has been given many different common names. When the larva consumes cotton, it is known as the cotton bollworm...
.
Distribution
This species is widespread in mid and south Europe, temperate Asia, Africa, Australia and Oceania. It is a migrant species, able to reach Scandinavia and other northern territories.Morphology
Life cycle
The female cotton bollworm can lay several hundred eggs, distributed on various parts of the plant. Under favourable conditions, the larvae can hatch within three days and the whole life cycle can be completed in just over a month.The eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
are spherical, 0.4 to 0.6 milimetres in diameter and have a costate surface. They are white, later becoming greenish.
The larvae
Larvae
In Roman mythology, lemures were shades or spirits of the restless or malignant dead, and are probably cognate with an extended sense of larvae as disturbing or frightening...
take thirteen to twenty two days to develop, reaching up to forty milimetres long in the sixth instar
Instar
An instar is a developmental stage of arthropods, such as insects, between each molt , until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form. Differences between instars can often be seen in altered body proportions, colors, patterns, or...
. Their colouring is variable but mostly greenish and yellow to red-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 ventral parts of the larvae are pale. They are rather aggressive, occasionally carnivorous and may even cannibalise each other. If disturbed they fall from the plant and curl up on the ground.
The pupae develop inside a silken cocoon
Cocoon
Cocoon may refer to:*Cocoon , a pupal casing made by moth caterpillars and other insect larvae*Apache Cocoon, web development software*Cocoon , a 1985 science fiction film**Cocoon: The Return, 1988 sequel to Cocoon...
over ten to fifteen days in soil at a depth of four to ten centimetres, or in cotton bolls or maize ears.
Host plants
The cotton bollworm is a highly polyphagous species. The most important crop hosts are tomato, cotton, pigeon pea, chickpea, 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, a number of fruit trees, forest trees and a range of vegetable crops. In Russia and adjacent countries, the larvae populate more than 120 plant species, favouring Solanum, Datura, Hyoscyamus, Atriplex and Amaranthus genera.Economic significance
The greatest damage is caused to cottonCotton
Cotton is a soft, fluffy staple fiber that grows in a boll, or protective capsule, around the seeds of cotton plants of the genus Gossypium. The fiber is almost pure cellulose. The botanical purpose of cotton fiber is to aid in seed dispersal....
, tomatoes, maize
Maize
Maize known in many English-speaking countries as corn or mielie/mealie, is a grain domesticated by indigenous peoples in Mesoamerica in prehistoric times. The leafy stalk produces ears which contain seeds called kernels. Though technically a grain, maize kernels are used in cooking as a vegetable...
, chick peas, alfalfa
Alfalfa
Alfalfa is a flowering plant in the pea family Fabaceae cultivated as an important forage crop in the US, Canada, Argentina, France, Australia, the Middle East, South Africa, and many other countries. It is known as lucerne in the UK, France, Australia, South Africa and New Zealand, and known as...
and tobacco
Tobacco
Tobacco is an agricultural product processed from the leaves of plants in the genus Nicotiana. It can be consumed, used as a pesticide and, in the form of nicotine tartrate, used in some medicines...
. The economic threshold of harmfulness in central Asia is three to five larvae per hundred plants of long-staple cotton and eight to twelve larvae per hundred plants on medium-staple cotton. In cotton crops, blooms that have been attacked may open prematurely and stay fruitless. When the bolls are damaged, some will fall off and others will fail to produce lint or produce lint of an inferior quality. Secondary infections by fungi and bacteria are common and may lead to rotting of 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 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 entomophages such as Trichogramma
Trichogramma
The wasps of genus Trichogramma, commonly known as "stingless wasps", are some of the most widely-studied agents of biological control in the field of entomology. Trichogramma wasps are tiny Hymenopteran insects, measuring 1 millimeter in length or less, that parasitize the eggs of many types of...
spp. and Habrobracon hebetor. Monitoring is possible by the use of sex pheromone
Pheromone
A pheromone is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting outside the body of the secreting individual to impact the behavior of the receiving individual...
traps.