(A. Schneider, 1859)
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.
Phasmarhabditis hermaphrodita can be detected and quantificated from soil samples by quantitative PCR. This method can also be used to distinguish it from the morphologically similar Phasmarhabditis neopapillosa.
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, bacteria 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 scavengers. The nematodes eat the cadaver and produce another generation of infective juveniles which move off through the soil in search of new slug hosts.
Biological control of slugs
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.
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