Phasmarhabditis hermaphrodita
Encyclopedia
Phasmarhabditis hermaphrodita is a microscopic nematode
in the family Rhabditidae
. It is a lethal parasite of the slug
, Deroceras reticulatum
and a large number of other slug species from the families Milacidae
, Limacidae
and Arionidae
. It is used as a molluscicide
for the biological control of these pests.
colonize their gut
. The juveniles actively search for potential slug hosts. When these are found, the nematodes enter through the breathing pore (pneumostome
) below the mantle
and move to the shell cavity. Here the bacteria are released and start multiplying and the nematodes feed on them and resume their growth. The bacteria cause septicaemia in the slug which develops a characteristic swelling of the mantle area and there is a marked reduction in its feeding activity. After between four and twenty one days, depending on the number of parasites and the temperature, the slug dies. The nematodes need several days to complete their life cycle and seem to be able to modify the host's behaviour so that it remains below the ground surface before death and is thus not readily available to predators and scavenger
s. The nematodes eat the cadaver
and produce another generation of infective juveniles which move off through the soil in search of new slug hosts.
instead of poisonous metaldehyde
or carbamates.
This nematode is commercially reared in a culture with the bacterium Moraxella osloensis
and sold as a biological molluscicide
. The culture is mixed with water and applied as a drench to the surface of the soil. This is best done at a soil temperature of about 15 °C, with a minimum of 5 °C and a maximum of 20 °C. The soil should be kept damp afterwards. Young seedlings and cuttings can best be protected by applying the nematodes one week in advance of sowing or planting. The protection is expected to last for at least six weeks. Because infection of the slug reduces its feeding activities, crop protection is rapid even before host mortality occurs.
It has been shown that when released, new generations of nematodes do not continue their symbiosis
with Moraxella osloensis but associate with a complex and variable mixture of other bacteria while still retaining their virulence.
In a study by Speiser et al. (2001), Phasmarhabditis hermaphrodita had little effect on larger specimen of Spanish slug
s.
Nematode
The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...
in the family Rhabditidae
Rhabditidae
Rhabditidae is a family of nematodes.-Genera:-Caenorhabditis:*Caenorhabditis brenneri Sudhaus & Kiontke, 2007*Caenorhabditis briggsae *Caenorhabditis dolichura *Caenorhabditis elegans Maupas, 1900*Caenorhabditis rara...
. It is a lethal parasite of the slug
Slug
Slug is a common name that is normally applied to any gastropod mollusc that lacks a shell, has a very reduced shell, or has a small internal shell...
, Deroceras reticulatum
Deroceras reticulatum
Deroceras reticulatum, common names "grey field slug" and "grey garden slug", is a species of small air-breathing land slug, a terrestrial pulmonate gastropod mollusk in the family Agriolimacidae...
and a large number of other slug species from the families Milacidae
Milacidae
Milacidae is a family of air-breathing, keeled, land slugs. These are shell-less terrestrial gastropod mollusks in the superfamily Parmacelloidea.This family has no subfamilies ....
, Limacidae
Limacidae
Limacidae, common name the keelback slugs, are a taxonomic family of medium-sized to very large, air-breathing land slugs, terrestrial pulmonate gastropod molluscs in the superfamily Limacoidea.- Distribution :...
and Arionidae
Arionidae
Arionidae, common name the "roundback slugs" or "round back slugs" are a taxonomic family of air-breathing land slugs, terrestrial pulmonate gastropod mollusks in the superfamily Arionoidea.- Distribution :...
. It is used as a molluscicide
Molluscicide
Molluscicides, also known as snail baits and snail pellets, are pesticides against molluscs, which are usually used in agriculture or gardening to control gastropod pests like slugs and snails that can damage crops by feeding on them....
for the biological control of these pests.
Description
Phasmarhabditis hermaphrodita can be detected and quantificated from soil samples by real-time PCR. This method can also be used to distinguish it from the morphologically similar Phasmarhabditis neopapillosa.Life cycle
Under natural conditions, infective juveniles of this species are found in the soil. They represent a stage in the development of the nematode which is specially adapted for survival in this unfavorable environment and while there, bacteriaBacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
colonize their gut
Gut (zoology)
In zoology, the gut, also known as the alimentary canal or alimentary tract, is a tube by which bilaterian animals transfer food to the digestion organs. In large bilaterians the gut generally also has an exit, the anus, by which the animal disposes of solid wastes...
. The juveniles actively search for potential slug hosts. When these are found, the nematodes enter through the breathing pore (pneumostome
Pneumostome
The pneumostome is a feature of the external body anatomy of an air-breathing land slug or land snail. It is a part of the respiratory system of gastropods....
) below the mantle
Mantle (mollusc)
The mantle is a significant part of the anatomy of molluscs: it is the dorsal body wall which covers the visceral mass and usually protrudes in the form of flaps well beyond the visceral mass itself.In many, but by no means all, species of molluscs, the epidermis of the mantle secretes...
and move to the shell cavity. Here the bacteria are released and start multiplying and the nematodes feed on them and resume their growth. The bacteria cause septicaemia in the slug which develops a characteristic swelling of the mantle area and there is a marked reduction in its feeding activity. After between four and twenty one days, depending on the number of parasites and the temperature, the slug dies. The nematodes need several days to complete their life cycle and seem to be able to modify the host's behaviour so that it remains below the ground surface before death and is thus not readily available to predators and scavenger
Scavenger
Scavenging is both a carnivorous and herbivorous feeding behavior in which individual scavengers search out dead animal and dead plant biomass on which to feed. The eating of carrion from the same species is referred to as cannibalism. Scavengers play an important role in the ecosystem by...
s. The nematodes eat the cadaver
Cadaver
A cadaver is a dead human body.Cadaver may also refer to:* Cadaver tomb, tomb featuring an effigy in the form of a decomposing body* Cadaver , a video game* cadaver A command-line WebDAV client for Unix....
and produce another generation of infective juveniles which move off through the soil in search of new slug hosts.
Biological control of slugs
Phasmarhabditis hermaphrodita can be used in organic farmingOrganic farming
Organic farming is the form of agriculture that relies on techniques such as crop rotation, green manure, compost and biological pest control to maintain soil productivity and control pests on a farm...
instead of poisonous metaldehyde
Metaldehyde
Metaldehyde is an organic compound with the formula 4. It is commonly used as a pesticide against slugs, snails, and other gastropods. It is the cyclic tetramer of acetaldehyde.-Production and properties:...
or carbamates.
This nematode is commercially reared in a culture with the bacterium Moraxella osloensis
Moraxella osloensis
Moraxella osloensis is a species of Gram-negative oxidase positive, aerobic bacteria within the family Moraxellaceae in the gamma subdivision of the purple bacteria....
and sold as a biological molluscicide
Molluscicide
Molluscicides, also known as snail baits and snail pellets, are pesticides against molluscs, which are usually used in agriculture or gardening to control gastropod pests like slugs and snails that can damage crops by feeding on them....
. The culture is mixed with water and applied as a drench to the surface of the soil. This is best done at a soil temperature of about 15 °C, with a minimum of 5 °C and a maximum of 20 °C. The soil should be kept damp afterwards. Young seedlings and cuttings can best be protected by applying the nematodes one week in advance of sowing or planting. The protection is expected to last for at least six weeks. Because infection of the slug reduces its feeding activities, crop protection is rapid even before host mortality occurs.
It has been shown that when released, new generations of nematodes do not continue their symbiosis
Symbiosis
Symbiosis is close and often long-term interaction between different biological species. In 1877 Bennett used the word symbiosis to describe the mutualistic relationship in lichens...
with Moraxella osloensis but associate with a complex and variable mixture of other bacteria while still retaining their virulence.
In a study by Speiser et al. (2001), Phasmarhabditis hermaphrodita had little effect on larger specimen of Spanish slug
Spanish slug
The Spanish slug, scientific name Arion vulgaris, more commonly known in English-speaking countries under the incorrectly applied Latin name, Arion lusitanicus, is a species of air-breathing land slug, a terrestrial pulmonate gastropod mollusk in the family Arionidae, the roundback slugs.This is a...
s.