Diamondback moth
Encyclopedia
The diamondback moth sometimes called cabbage moth, is a European moth believed to originate in the Mediterranean region that has since spread worldwide. The moth has a short life cycle (14 days at 25°C), is highly fecund and capable of migrating long distances. It is one of the most important pests of cruciferous crops in the world and will usually only feed on plants that produce glucosinolate
s. However, not all of these plants are equally useful as hosts to the moth; there has been some discussion of using wintercress
as a buffer plant around agricultural fields as diamondback moths are highly attracted to that plant but their eggs fail to survive when oviposited on it.
of about fifteen milimetres and a body length of six milimetres. The fore wings are narrow, brownish-gray and lighter along the anterior margin, with fine dark speckles. There is a creamy-coloured stripe with a wavy edge on the posterior margin. This band is sometimes constricted to form one or more light-colored diamond-shapes which is the basis for the common name of this moth. The hind wings are narrow, pointed toward the apex and light gray, with a wide fringe. The tips of the wings can be seen to turn upward slightly when viewed from the side. The antennae are pronounced. The life span averages three to four weeks for females but rather less for males. The moths are weak fliers seldom rising more than two metres above the ground and not flying long distances. They are however passive migrants, being easily transferred by wind over long distances. Diamondback moths overwinter as adults among field debris of cruciferous crops and active adults may be seen during warm periods at any time during the winter in temperate areas. They do not survive cold winters and re-invade colder areas each spring being carried there by the wind. Moths are active usually at twilight and at night, feeding on flowers of cruciferous plants but they also fly in the afternoon during mass outbreaks.
The eggs
are oval and flattened, measuring 0.44 milimetres long and 0.26 milimetres wide. They are yellow or pale green at first but darken later. They are laid singly or in groups of two to eight eggs in depressions on the surface of leaves. Females may deposit up to 300 eggs in total but average production is probably half that amount. The larvae emerge from the eggs in about six days.
The larvae
have four instars, each with an average development time of about four days. The larval body form tapers at both ends. The larvae have a few short black hairs and are colourless in the first instar but pale or emerald green with black heads in later instars. There are five pairs of prolegs, one of which protrudes from the posterior end forming a distinctive "V". The larvae are quite active and when disturbed may wriggle violently, move backward and spin a strand of silk from which to dangle. The feeding habit of the first instar is leaf mining although they are so small that the mines are difficult to detect. The larvae emerge from these mines to moult
and subsequently feed on the lower surface of the leaf. Their chewing results in irregular patches of damage though the upper leaf epidermis
is often left intact.
The yellowish pupae are about eight milimetres long and are wrapped in a loose silk cocoon
. They are usually found on the lower or outer leaves of the food plant but on cauliflower and broccoli, pupation may occur in the florets. The pupal stage lasts on average for about eight days but ranges from five to fifteen days.
. Nearly all cruciferous vegetable crops are attacked but some are favoured over others. These include broccoli, Brussels sprouts, cabbage, Chinese cabbage, cauliflower, collard, kale, kohlrabi, mustard, radish, turnip and watercress. Several wild species in the family also act as hosts, especially early in the season when cultivated crops are unavailable.
plants. Although the larvae are small, they can be very numerous and cause complete removal of foliar tissue except for the leaf veins. This is damaging to young seedlings and may disrupt head formation in cabbage, broccoli and cauliflower. The presence of larvae in florets can result in complete rejection of the produce. The diamondback moth is considered a pest in areas that do not experience very cold winters, as these help to kill off overwintering moths. Control used to be through the use of chemical insecticides but in the 1980s resistance developed to pyrethroid
s and soon afterwards, virtually all insecticides became ineffective. A decrease in insecticide use, and particularly elimination of pyrethroid use, can help by favoring survival of the parasitoids, Microplitis plutellae, Diadegma insulare and Diadromus subtilicornis. The parasitoid Cotesia plutellae is reared in laboratories and released for the control of diamondback moth as part of Integrated Pest Management programmes in several countries (e.g; Mauritius).
The diamondback moth was the first insect that was found to have become resistant to biological control by the Bt toxin
(Bacillus thuringiensis) in the field. Trichoplusia ni (Cabbage looper
) is the only other insect to have developed resistance to Bt toxin in agricultural systems, specifically in greenhouses.
Glucosinolate
The glucosinolates are a class of organic compounds that contain sulfur and nitrogen and are derived from glucose and an amino acid. They occur as secondary metabolites of almost all plants of the order Brassicales , but also in the genus Drypetes .-Chemistry:Glucosinolates are water-soluble...
s. However, not all of these plants are equally useful as hosts to the moth; there has been some discussion of using wintercress
Barbarea vulgaris
Barbarea vulgaris, also called as Bittercress, Herb Barbara, Rocketcress, Yellow Rocketcress, Winter Rocket, and Wound Rocket, is a biennial herb of the genus Barbarea, belonging to the family Brassicaceae....
as a buffer plant around agricultural fields as diamondback moths are highly attracted to that plant but their eggs fail to survive when oviposited on it.
Distribution
The diamondback moth has a global distribution and is found in Europe, Asia, Africa, the Americas, Australia, New Zealand and the Hawaiian islands. It probably originated in Europe and was first observed in North America in 1854, in Illinois. It had spread to Florida and the Rocky Mountains by 1883 and was reported from British Columbia by 1905.Morphology
The diamondback moth has a wingspanWingspan
The wingspan of an airplane or a bird, is the distance from one wingtip to the other wingtip. For example, the Boeing 777 has a wingspan of about ; and a Wandering Albatross caught in 1965 had a wingspan of , the official record for a living bird.The term wingspan, more technically extent, is...
of about fifteen milimetres and a body length of six milimetres. The fore wings are narrow, brownish-gray and lighter along the anterior margin, with fine dark speckles. There is a creamy-coloured stripe with a wavy edge on the posterior margin. This band is sometimes constricted to form one or more light-colored diamond-shapes which is the basis for the common name of this moth. The hind wings are narrow, pointed toward the apex and light gray, with a wide fringe. The tips of the wings can be seen to turn upward slightly when viewed from the side. The antennae are pronounced. The life span averages three to four weeks for females but rather less for males. The moths are weak fliers seldom rising more than two metres above the ground and not flying long distances. They are however passive migrants, being easily transferred by wind over long distances. Diamondback moths overwinter as adults among field debris of cruciferous crops and active adults may be seen during warm periods at any time during the winter in temperate areas. They do not survive cold winters and re-invade colder areas each spring being carried there by the wind. Moths are active usually at twilight and at night, feeding on flowers of cruciferous plants but they also fly in the afternoon during mass outbreaks.
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 oval and flattened, measuring 0.44 milimetres long and 0.26 milimetres wide. They are yellow or pale green at first but darken later. They are laid singly or in groups of two to eight eggs in depressions on the surface of leaves. Females may deposit up to 300 eggs in total but average production is probably half that amount. The larvae emerge from the eggs in about six days.
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...
have four instars, each with an average development time of about four days. The larval body form tapers at both ends. The larvae have a few short black hairs and are colourless in the first instar but pale or emerald green with black heads in later instars. There are five pairs of prolegs, one of which protrudes from the posterior end forming a distinctive "V". The larvae are quite active and when disturbed may wriggle violently, move backward and spin a strand of silk from which to dangle. The feeding habit of the first instar is leaf mining although they are so small that the mines are difficult to detect. The larvae emerge from these mines to moult
Moult
In biology, moulting or molting , also known as sloughing, shedding, or for some species, ecdysis, is the manner in which an animal routinely casts off a part of its body , either at specific times of year, or at specific points in its life cycle.Moulting can involve the epidermis , pelage...
and subsequently feed on the lower surface of the leaf. Their chewing results in irregular patches of damage though the upper leaf epidermis
Epidermis (botany)
The epidermis is a single-layered group of cells that covers plants' leaves, flowers, roots and stems. It forms a boundary between the plant and the external environment. The epidermis serves several functions, it protects against water loss, regulates gas exchange, secretes metabolic compounds,...
is often left intact.
The yellowish pupae are about eight milimetres long and are wrapped in a loose silk 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...
. They are usually found on the lower or outer leaves of the food plant but on cauliflower and broccoli, pupation may occur in the florets. The pupal stage lasts on average for about eight days but ranges from five to fifteen days.
Host plants
The diamondback moth lays its eggs only on plants in the family BrassicaceaeBrassicaceae
Brassicaceae, a medium sized and economically important family of flowering plants , are informally known as the mustards, mustard flowers, the crucifers or the cabbage family....
. Nearly all cruciferous vegetable crops are attacked but some are favoured over others. These include broccoli, Brussels sprouts, cabbage, Chinese cabbage, cauliflower, collard, kale, kohlrabi, mustard, radish, turnip and watercress. Several wild species in the family also act as hosts, especially early in the season when cultivated crops are unavailable.
Economic significance
Larvae damage leaves, buds, flowers, and seed-buds of cultivated cruciferousBrassicaceae
Brassicaceae, a medium sized and economically important family of flowering plants , are informally known as the mustards, mustard flowers, the crucifers or the cabbage family....
plants. Although the larvae are small, they can be very numerous and cause complete removal of foliar tissue except for the leaf veins. This is damaging to young seedlings and may disrupt head formation in cabbage, broccoli and cauliflower. The presence of larvae in florets can result in complete rejection of the produce. The diamondback moth is considered a pest in areas that do not experience very cold winters, as these help to kill off overwintering moths. Control used to be through the use of chemical insecticides but in the 1980s resistance developed to pyrethroid
Pyrethroid
A pyrethroid is an organic compound similar to the natural pyrethrins produced by the flowers of pyrethrums . Pyrethroids now constitute a major commercial household insecticides...
s and soon afterwards, virtually all insecticides became ineffective. A decrease in insecticide use, and particularly elimination of pyrethroid use, can help by favoring survival of the parasitoids, Microplitis plutellae, Diadegma insulare and Diadromus subtilicornis. The parasitoid Cotesia plutellae is reared in laboratories and released for the control of diamondback moth as part of Integrated Pest Management programmes in several countries (e.g; Mauritius).
The diamondback moth was the first insect that was found to have become resistant to biological control by the Bt toxin
Bacillus thuringiensis
Bacillus thuringiensis is a Gram-positive, soil-dwelling bacterium, commonly used as a biological pesticide; alternatively, the Cry toxin may be extracted and used as a pesticide. B...
(Bacillus thuringiensis) in the field. Trichoplusia ni (Cabbage looper
Cabbage looper
The Cabbage Looper is a member of the moth family Noctuidae. It is found throughout the southern Palaearctic ecozone, all of North America, parts of Africa and most of the Oriental and Indo-Australian region....
) is the only other insect to have developed resistance to Bt toxin in agricultural systems, specifically in greenhouses.
External links
- diamondback moth on the UFUniversity of FloridaThe University of Florida is an American public land-grant, sea-grant, and space-grant research university located on a campus in Gainesville, Florida. The university traces its historical origins to 1853, and has operated continuously on its present Gainesville campus since September 1906...
/ IFASInstitute of Food and Agricultural SciencesThe University of Florida’s Institute of Food and Agricultural Sciences is a federal-state-county partnership dedicated to developing knowledge in agriculture, human and natural resources, and the life sciences, and enhancing and sustaining the quality of human life by making that information...
Featured Creatures Web site - http://lepidoptera.butterflyhouse.com.au/plut/xylost.html University of Technology, Sydney.