The relative importance of the factors driving change in the population dynamics of nematodes in the soil is almost completely unknown. Top‐down control by micro‐arthropod predators may have a ...significant impact on nematode population dynamics. We report experiments showing that mites and Collembola were capable of reducing nematode numbers in the laboratory and were feeding on a targeted nematode species in the field. A PCR‐based approach was developed for the detection of predation on three species of slug‐ and insect‐pathogenic nematodes: Phasmarhabditis hermaphrodita, Heterorhabditis megidis and Steinernema feltiae. The collembolan Folsomia candida and the mesostigmatid mite Stratiolaelaps miles were employed as model predators to calibrate post‐ingestion prey DNA detection times. Fragments of cytochrome oxidase I (COI) mtDNA were sequenced and species‐specific primers were designed, amplifying 154‐, 154‐ and 203‐bp fragments for each of the nematode species. Detection times for nematode DNA within the guts of Collembola were longer than in mites, with half‐lives (50% of samples testing positive) of 08.75 h and 05.03 h, respectively. F. candida significantly reduced numbers of the nematode H. megidis, with rates of predation of ∼0.4 nematode infective juveniles per collembolan per hour over 10 h. Four taxa of field‐caught micro‐arthropod that had been exposed to the nematode P. hermaphrodita for a period of 12 h were analysed and significant numbers of three taxa tested positive. This is the first application of PCR techniques for the study of nematophagy and the first time these techniques have been used to measure predation on nematodes in the field.
This paper compares efficiency of preparations based on a parasitic nematode species Phasmarhabditis hermaphrodita with a molluscocide containing methiocarb as an effective substance. Parasitic ...nematodes by the family Agriolimacidae showed a significantly better effect on mortality and reduction of the percentage of damaged plants than the methiocarb-based preparation. Under laboratory and field conditions, the efficiency of parasitic nematodes on the family Agriolimacidae ranged from 84% to 94% and from 81% to 94%, resp., while the percentages of damaged plants were minimal in both cases. The corresponding effects of the methiocarb-based molluscocide were only 35% and 21%, resp. The effect of parasitic P. hermaphrodita nematodes on members of the snail family Arionidae was not demonstrated both under laboratory and field conditons and the mortality was up to 6% with a total defoliation of plants. Under laboratory and field conditions, the mortality of slugs from the genus Arion after the application of methiocarb-based preparation was 53% and 38%, resp. However, the damage of plants was significant and it reached nearly 67% and 60% under laboratory and field conditions, resp.
The rhabditid nematode, Phasmarhabditis hermaphrodita is a lethal parasite of certain terrestrial gastropods and has been shown as a biocontrol agent under laboratory and field conditions. In Egypt, ...P. hermaphrodita was isolated for the first time from different species of terrestrial gastropods found associated with various crops at Aga and Mansoura districts of Dakhalia Governorate during the year 2000/2001. Females and dauer larvae (IJs) were described and illustrated based on the light microscope. Males are not found as this species seemed to be protandrous. PCR analysis confirmed nematode identification. The Egyptian isolate of P. hermaphrodita was found to be shorter and lower in width than the British isolate. V%, a, b and c parameters showed detectable variations between two isolates with values of 54%, 17.7, 4.28, 13.7 in the Egyptian isolate, and 51%, 19.5, 7.2 and 15.8 for the British isolate, respectively.
The nematode Phasmarhabditis hermaphrodita is the only commercial biological control agent for terrestrial slugs. We investigated whether the predicted conditions of winter warming could have any ...effect on its performance. In the presence of nematodes, slug damage to lettuce plants and slug survival were significantly lower under the predicted conditions of winter warming than under normal winter conditions, while in the absence of nematodes, slug damage and survival were similar under the conditions of winter warming and under current winter conditions. The data suggest that P. hermaphrodita may perform better under the predicted conditions of winter warming.
The dynamics of predation on parasites within prey has received relatively little attention despite the profound effects this is likely to have on both prey and parasite numbers and hence on ...biological control programmes where parasites are employed. The nematode Phasmarhabditis hermaphrodita is a commercially available biological agent against slugs. Predation on these slugs may, at the same time, result in intraguild predation on slug-parasitic nematodes. This study describes, for the first time, predation by carabid beetles on slugs and their nematode parasites on both spatial and temporal scales, using PCR-based methods. The highest nematode infection levels were found in the slugs Deroceras reticulatum and Arion silvaticus. Numbers of infected slugs decreased over time and no infected slugs were found four months after nematode application. The density of the most abundant slug, the invasive Arion vulgaris, was positively related to the activity-density of the carabid beetle, Carabus nemoralis. Predation on slugs was density and size related, with highest predation levels also on A. vulgaris. Predation on A. vulgaris decreased significantly in summer when these slugs were larger than one gram. Predation by C. nemoralis on slugs was opportunistic, without any preferences for specific species. Intraguild predation on the nematodes was low, suggesting that carabid beetles such as C. nemoralis probably do not have a significant impact on the success of biological control using P. hermaphrodita.
Phasmarhabditis hermaphrodita is a nematode parasite of slugs that is commercially reared in monoxenic culture with the bacterium
Moraxella osloensis and sold as a biological molluscicide. However, ...its bacterial associations when reared
in vivo in slugs are unknown. We show that when reared
in vivo in slugs,
P. hermaphrodita does not retain
M. osloensis and associates with complex and variable bacterial assemblages that do not influence its virulence. This is in marked contrast to the entomopathogenic nematodes that form highly specific mutualistic associations with Enterobacteriaceae that are specifically retained during
in vivo growth.
Slugs are serious pests of a range of crops worldwide and are commonly controlled using chemical bait molluscicides.
Phasmarhabditis hermaphrodita is a slug parasitic nematode that can be an ...effective alternative to chemical pellets. We conducted a field trial with Chinese cabbage to assess the potential of new nematode application techniques (dipping of root plugs, spraying around plant base and three low doses of
P. hermaphrodita) compared to standard broadcast spraying of nematodes and chemical molluscicides. We also performed a series of miniplot trials investigating persistence of
P. hermaphrodita, the efficacy of
P. hermaphrodita compared to chemical molluscicides (iron phosphate and metaldehyde pellets) and using three repeated low doses of
P. hermaphrodita compared to one broadcast spraying treatment. In field trials new application strategies of three low doses of
P. hermaphrodita and dipping the plant roots in
P. hermaphrodita reduced slug damage but did not reduce slug numbers. In miniplot trials we found that
P. hermaphrodita persisted in soil and caused significant slug control 38
days after initial application. Also three low dose applications of
P. hermaphrodita provided slug control comparable to one broadcast spraying. Also, we found that new chemical molluscicides such as iron phosphate can significantly reduce slug damage caused by
Deroceras reticulatum and
Arion ater.
The life cycle of commercially used molluscicidal rhabditid nematodes
Phasmarhabditis hermaphrodita and entomopathogenic steinernematid nematodes is similar: infective stages carry symbiotic ...bacteria, which kill their host. Nematodes complete their life cycle feeding on the proliferating symbiont and the host tissue. After 1–2 weeks, new infective stages carrying the bacteria leave the host cadaver in search of new hosts. The removal of invertebrate cadavers by scavengers is extremely fast and represents a severe threat to the developing nematodes.Two-choice trials were used to assess prey choice of the generalist predator/scavenger
Pterostichus melanarius (Coleoptera: Carabidae) between
Deroceras reticulatum (Mollusca: Agriolimacidae) slugs or wax moth
Galleria mellonella (Lepidoptera: Pyralidae) larvae killed by infection of
P. hermaphrodita/
Steinernema affine and control killed by freezing. We demonstrate that the presence of either of the two nematodes tested deters the beetles from consuming infected cadavers. As
P. hermaprodita cannot infect an insect host, we hypothesise the deterrent effect being an evolutionary adaptation of the nematode/bacteria complex rather than the ability of the beetles to avoid potentially infective cadavers.
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