Wattle bagworm
Encyclopedia
The Wattle bagworm is a species of moth
in the family Psychidae. In Southern Africa
it is a pest of the Black Wattle, Acacia mearnsii, which is grown largely as a source of vegetable tannin
. Kotochalia junodi is indigenous to Southern Africa, where it originally fed on indigenous relatives of the wattle.
Like all members of the family Psychidae, the male larva
develops into an adult in a mobile silk
en bag covered with materials such as thorns and twigs. Only once it is mature does it leave the bag to mate. The female never leaves her bag.
In spring the eggs hatch in the bag in which the adult female had grown. Because the female never leaves the tree in which she grew and died, the insects need some other way to move to new trees or in general to disperse
, and in fact the newly hatched (first-instar
) larva is the dispersive
stage of the wattle bagworm life cycle. The larva spins a silken thread on which it may float along on the breeze, much as some species of young spiderlings use gossamer
for ballooning
in their dispersive phase. Also, birds and probably other agencies may carry some larvae to suitable feeding sites. The young caterpillar does not feed for a day or two after hatching, but eventually, once the dispersive phase is completed, it begins to weave a conical bag of silk, incorporating fragments of plant material such as leaves, twigs and bark.
The thorns and twigs covering the cocoon provide protection against enemies such as mantids. They also serve as camouflage
that matches the tree from which the larva had stripped them. As it feeds and grows, it extends the size of the bag until it reaches some 55 mm in length and 18 mm in width and its outline becomes oval. The caterpillar hooks its anal prolegs into the silken lining of the bag. As it feeds and grows, the larva drags the bag wherever it goes until it is full grown and pupates. If alarmed, it shuts the opening by pulling in the slack in front.
About February or March the larva is fully grown. It stops feeding, fastens its bag to the tree, and spins an inner lining within which it pupates. The males pupate in April or May and the females perhaps a month later. The winged male emerges from its cocoon some time between August and October. The male does not feed after emerging, and lives for only a few days. It has wings almost clear of scales and flies strongly, seeking out a mature female to inseminate. The female in contrast, remains in her bag after emerging from the pupa. She is a highly specialised, worm-like creature: she has no wings at all, and lacks legs and even eyes; she lies helpless in her shelter, only able to turn her posterior towards the opening of her bag for insemination, and away from the opening for oviposition
. The male inserts the point of his abdomen
through the neck of the bag and inseminates her. Oviposition
starts immediately afterwards, sometimes even before insemination, and in mid- or late winter successful females produces on average about 1600 eggs. They remain in the bag together with the shrunken remains of the mother, hatching about two months later.
This relatively large clutch
size reflects the fact that on average only a few of the larvae survive to reproduce.
The large number of eggs is at least in part an adaptation
to the female's inability to fly and the compensatory strategy
for dispersion of the newly hatched larvae; wattle bagworm larvae rely on an unusual mode of transport. After hatching as a caterpillar, the insect spins a silk thread and hangs from the end for a few days. The wind or a passing bird sometimes transports the caterpillar to another tree, spreading the species quite effectively, if inefficiently. Given the large number of eggs, there is a reasonable chance that at least some of them will find adventitious transport. The rest either starve, or settle down in the tree where they hatched which is likely to die from defoliation within a few seasons if natural or artificial controls do not prevent.
The wattle bagworm has many natural enemies. They include parasitic wasps, flies and beetles, and various predators, such as spiders and birds, not to mention fungal diseases such as Entomophthora and Isaria species, bacterial diseases such as Bacillus thuringiensis
, and polyhedral virus diseases. Attempts to use such a virus for bagworm control during the 1950s gave results too inconsistent to be satisfactory at the time.
In the wild probably the most important insect enemy of Kotochalia junodi is an interesting parasitoid
wasp, a member of the Ichneumonidae
, Sericopimpla sericata. In colour the wasp is largely black, yellowish, and red. The female wasp is about 12 mm in length, and like many Ichneumonids she has a protruding ovipositor
almost as long as her gaster
.
A surprising feature of Sericopimpla sericata habits is that the adult kills bagworms in two ways. In either case it stings them with the ovipositor. The bagworm wriggles and contorts within the bag to avoid attack, but as a rule the female wasp succeeds in stinging it sooner or later. In some cases the female then proceeds to eat the prey herself. The sting paralyses the victim, and the wasp bites a hole in the bag and feeds
through it. Such predatory feeding by parasitoids is very unusual. No doubt the female needs the plentiful fat and protein of the victim to produce eggs, much as many blood-sucking female insects need a blood meal before they can lay eggs.
An adequately nourished female will parasitise the bagworm with several stings, perhaps dozens. Paralysed hosts remain fresh for months, long enough for the wasp larvae.
The bagworm routinely infest
s the large local wattle
plantations, which cover more than half a million acres (2,000 km²) in South Africa
, primarily in Natal. Natural control of the bagworm is variable, but good enough that the use of the most dangerous insecticides has effectively been discontinued. Nowadays the policy is to spray only heavy infestations, and only at strategic times. In the mid-20th century chlorinated hydrocarbon insecticides such as toxaphene
and endrin
were the treatments of choice for control of wattle bagworm infestations, but since then the preference has shifted to the bacterial insecticide BTK
. For small infestations or localized impact, "manual control" -- simply picking bags from the trees—may be satisfactory.
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...
in the family Psychidae. In Southern Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
it is a pest of the Black Wattle, Acacia mearnsii, which is grown largely as a source of vegetable tannin
Tannin
A tannin is an astringent, bitter plant polyphenolic compound that binds to and precipitates proteins and various other organic compounds including amino acids and alkaloids.The term tannin refers to the use of...
. Kotochalia junodi is indigenous to Southern Africa, where it originally fed on indigenous relatives of the wattle.
Like all members of the family Psychidae, the male larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
develops into an adult in a mobile silk
Silk
Silk is a natural protein fiber, some forms of which can be woven into textiles. The best-known type of silk is obtained from the cocoons of the larvae of the mulberry silkworm Bombyx mori reared in captivity...
en bag covered with materials such as thorns and twigs. Only once it is mature does it leave the bag to mate. The female never leaves her bag.
In spring the eggs hatch in the bag in which the adult female had grown. Because the female never leaves the tree in which she grew and died, the insects need some other way to move to new trees or in general to disperse
Biological dispersal
Biological dispersal refers to species movement away from an existing population or away from the parent organism. Through simply moving from one habitat patch to another, the dispersal of an individual has consequences not only for individual fitness, but also for population dynamics, population...
, and in fact the newly hatched (first-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...
) larva is the dispersive
Biological dispersal
Biological dispersal refers to species movement away from an existing population or away from the parent organism. Through simply moving from one habitat patch to another, the dispersal of an individual has consequences not only for individual fitness, but also for population dynamics, population...
stage of the wattle bagworm life cycle. The larva spins a silken thread on which it may float along on the breeze, much as some species of young spiderlings use gossamer
Spider silk
Spider silk is a protein fiber spun by spiders. Spiders use their silk to make webs or other structures, which function as nets to catch other animals, or as nests or cocoons for protection for their offspring...
for ballooning
Ballooning (spider)
Ballooning is a term used for the mechanical kiting that many spiders, especially small species, as well as certain mites and some caterpillars use to disperse through the air. Many small spiders use gossamer or especially fine silk to lift themselves off a surface or use the silk as an anchor in...
in their dispersive phase. Also, birds and probably other agencies may carry some larvae to suitable feeding sites. The young caterpillar does not feed for a day or two after hatching, but eventually, once the dispersive phase is completed, it begins to weave a conical bag of silk, incorporating fragments of plant material such as leaves, twigs and bark.
The thorns and twigs covering the cocoon provide protection against enemies such as mantids. They also serve as camouflage
Camouflage
Camouflage is a method of concealment that allows an otherwise visible animal, military vehicle, or other object to remain unnoticed, by blending with its environment. Examples include a leopard's spotted coat, the battledress of a modern soldier and a leaf-mimic butterfly...
that matches the tree from which the larva had stripped them. As it feeds and grows, it extends the size of the bag until it reaches some 55 mm in length and 18 mm in width and its outline becomes oval. The caterpillar hooks its anal prolegs into the silken lining of the bag. As it feeds and grows, the larva drags the bag wherever it goes until it is full grown and pupates. If alarmed, it shuts the opening by pulling in the slack in front.
About February or March the larva is fully grown. It stops feeding, fastens its bag to the tree, and spins an inner lining within which it pupates. The males pupate in April or May and the females perhaps a month later. The winged male emerges from its cocoon some time between August and October. The male does not feed after emerging, and lives for only a few days. It has wings almost clear of scales and flies strongly, seeking out a mature female to inseminate. The female in contrast, remains in her bag after emerging from the pupa. She is a highly specialised, worm-like creature: she has no wings at all, and lacks legs and even eyes; she lies helpless in her shelter, only able to turn her posterior towards the opening of her bag for insemination, and away from the opening for oviposition
Oviposition
Oviposition is the process of laying eggs by oviparous animals.Some arthropods, for example, lay their eggs with an organ called the ovipositor.Fish , amphibians, reptiles, birds and monetremata also lay eggs....
. The male inserts the point of his abdomen
Abdomen
In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...
through the neck of the bag and inseminates her. Oviposition
Oviposition
Oviposition is the process of laying eggs by oviparous animals.Some arthropods, for example, lay their eggs with an organ called the ovipositor.Fish , amphibians, reptiles, birds and monetremata also lay eggs....
starts immediately afterwards, sometimes even before insemination, and in mid- or late winter successful females produces on average about 1600 eggs. They remain in the bag together with the shrunken remains of the mother, hatching about two months later.
This relatively large clutch
Clutch (eggs)
A clutch of eggs refers to all the eggs produced by birds or reptiles, often at a single time, particularly those laid in a nest.In birds, destruction of a clutch by predators, , results in double-clutching...
size reflects the fact that on average only a few of the larvae survive to reproduce.
The large number of eggs is at least in part an adaptation
Adaptation
An adaptation in biology is a trait with a current functional role in the life history of an organism that is maintained and evolved by means of natural selection. An adaptation refers to both the current state of being adapted and to the dynamic evolutionary process that leads to the adaptation....
to the female's inability to fly and the compensatory strategy
Strategy (game theory)
In game theory, a player's strategy in a game is a complete plan of action for whatever situation might arise; this fully determines the player's behaviour...
for dispersion of the newly hatched larvae; wattle bagworm larvae rely on an unusual mode of transport. After hatching as a caterpillar, the insect spins a silk thread and hangs from the end for a few days. The wind or a passing bird sometimes transports the caterpillar to another tree, spreading the species quite effectively, if inefficiently. Given the large number of eggs, there is a reasonable chance that at least some of them will find adventitious transport. The rest either starve, or settle down in the tree where they hatched which is likely to die from defoliation within a few seasons if natural or artificial controls do not prevent.
The wattle bagworm has many natural enemies. They include parasitic wasps, flies and beetles, and various predators, such as spiders and birds, not to mention fungal diseases such as Entomophthora and Isaria species, bacterial diseases such as Bacillus thuringiensis
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...
, and polyhedral virus diseases. Attempts to use such a virus for bagworm control during the 1950s gave results too inconsistent to be satisfactory at the time.
In the wild probably the most important insect enemy of Kotochalia junodi is an interesting parasitoid
Parasitoid
A parasitoid is an organism that spends a significant portion of its life history attached to or within a single host organism in a relationship that is in essence parasitic; unlike a true parasite, however, it ultimately sterilises or kills, and sometimes consumes, the host...
wasp, a member of the Ichneumonidae
Ichneumonidae
Ichneumonidae is a family within the insect order Hymenoptera. Insects in this family are commonly called ichneumon wasps. Less exact terms are ichneumon flies , or scorpion wasps due to the extreme lengthening and curving of the abdomen...
, Sericopimpla sericata. In colour the wasp is largely black, yellowish, and red. The female wasp is about 12 mm in length, and like many Ichneumonids she has a protruding ovipositor
Ovipositor
The ovipositor is an organ used by some animals for oviposition, i.e., the laying of eggs. It consists of a maximum of three pairs of appendages formed to transmit the egg, to prepare a place for it, and to place it properly...
almost as long as her gaster
Gaster
The gaster is the bulbous posterior portion of the metasoma found in Apocrita Hymenoptera . This begins with abdominal segment III on most ants, but some make a postpetiole out of segment III, in which case the gaster begins with abdominal segment IV....
.
A surprising feature of Sericopimpla sericata habits is that the adult kills bagworms in two ways. In either case it stings them with the ovipositor. The bagworm wriggles and contorts within the bag to avoid attack, but as a rule the female wasp succeeds in stinging it sooner or later. In some cases the female then proceeds to eat the prey herself. The sting paralyses the victim, and the wasp bites a hole in the bag and feeds
through it. Such predatory feeding by parasitoids is very unusual. No doubt the female needs the plentiful fat and protein of the victim to produce eggs, much as many blood-sucking female insects need a blood meal before they can lay eggs.
An adequately nourished female will parasitise the bagworm with several stings, perhaps dozens. Paralysed hosts remain fresh for months, long enough for the wasp larvae.
The bagworm routinely infest
Infest
Infest may refer to:*Infest can mean to overly populate, much in the same way that cockroaches do. See Overpopulation #Wild animal overpopulation.*Infest , a 2000 hard rock album by Papa Roach*Infest , American hardcore band...
s the large local wattle
Acacia
Acacia is a genus of shrubs and trees belonging to the subfamily Mimosoideae of the family Fabaceae, first described in Africa by the Swedish botanist Carl Linnaeus in 1773. Many non-Australian species tend to be thorny, whereas the majority of Australian acacias are not...
plantations, which cover more than half a million acres (2,000 km²) in South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
, primarily in Natal. Natural control of the bagworm is variable, but good enough that the use of the most dangerous insecticides has effectively been discontinued. Nowadays the policy is to spray only heavy infestations, and only at strategic times. In the mid-20th century chlorinated hydrocarbon insecticides such as toxaphene
Toxaphene
Toxaphene is an insecticide. It is a mixture of closely related substances whose use is now banned in most of the world due to concerns of toxicity.-Composition:...
and endrin
Endrin
Endrin is an organochloride that was primarily used as an insecticide. It is a colourless odorless solid, although commercial samples are often off-white. It is also a rodenticide. This compound became infamous as persistent organic pollutant and for this reason is banned in many...
were the treatments of choice for control of wattle bagworm infestations, but since then the preference has shifted to the bacterial insecticide BTK
BTK
BTK may refer to:*Baku-Tbilisi-Kars Railway*Dennis Rader, a serial killer known as the "BTK killer"**"Bind Torture Kill", a song by the band Suffocation on its album Suffocation....
. For small infestations or localized impact, "manual control" -- simply picking bags from the trees—may be satisfactory.