Recent stable isotope analyses indicate that a number of putative detritivorous soil microarthropods is not typical detritivores but rather live as predators or scavengers. Using molecular gut ...content analyses the present study investigates if nematodes indeed form part of the diet of oribatid mites. First, in a no-choice laboratory feeding experiment two nematode species (
Phasmarhabditis hermaphrodita and
Steinernema feltiae) were offered to eight species of oribatid mites and one gamasid mite. Second, after feeding for 4 and 48
h on each nematode species the detection time of prey DNA in the oribatid mite species
Steganacarus magnus was investigated. Third, in a field experiment nematode prey (
P. hermaphrodita and
S. feltiae) in the diet of microarthropods was investigated distinguishing between scavenging and predation. In the no-choice laboratory experiment not only the gamasid mite but also several of the studied oribatid mite species consumed nematodes. After feeding on nematodes for 4
h prey DNA was detectable in
S. magnus for only 4
h, but after feeding for 48
h prey DNA was detectable for 128
h, indicating that the duration of feeding on prey is an important determinant for prey DNA detection. The field experiment confirmed that oribatid mite species including
Liacarus subterraneus,
Platynothrus peltifer and
S. magnus intensively prey on nematodes. Interestingly, DNA of dead
P. hermaphrodita was detectable to a similar degree as that of living individuals indicating that scavenging is of significant importance in decomposer food webs. Results of our study indicate that predation and scavenging on nematodes by “detritivorous” microarthropods in soil food webs need to be reconsidered.
► Oribatid mites prey on nematodes and prey DNA is identified in their gut. ► Oribatid species vary in the extent to which they consume nematodes. ► Molecular gut content analyses were used to distinguish between predation and scavenging in the field.
The gastropod parasitic nematode Phasmarhabditis hermaphrodita has been formulated into a successful biological control agent (Nemaslug®, strain DMG0001) used to kill slugs on farms and gardens. When ...applied to soil, P. hermaphrodita uses slug mucus and faeces to find potential hosts. However, there is little information on what cues other species of Phasmarhabditis (P. neopapillosa and P. californica) use to find hosts and whether there is natural variation in their ability to chemotax to host cues. Therefore, using chemotaxis assays, we exposed nine wild isolates of P. hermaphrodita, five isolates of P. neopapillosa and three isolates of P. californica to mucus from the pestiferous slug host Deroceras invadens, as well as 1% and 5% hyaluronic acid – a component of slug mucus that is highly attractive to these nematodes. We found P. hermaphrodita (DMG0010) and P. californica (DMG0018) responded significantly more to D. invadens mucus and 1% hyaluronic acid than other strains. Also, P. hermaphrodita (DMG0007), P. neopapillosa (DMG0015) and P. californica (DMG0017) were superior at locating 5% hyaluronic acid compared to other isolates of the same genera. Ultimately, there is natural variation in chemoattraction in Phasmarhabditis nematodes, with some strains responding significantly better to host cues than others.
Summary
Phasmarhabditis hermaphrodita is a lethal parasite of several slug species and has been formulated into a biological control agent for farmers and gardeners. Phasmarhabditis hermaphrodita ...responds to slug faeces, mucus and volatile cues to find hosts in soil. However, these results have only focused on one strain of P. hermaphrodita (DMG0001). We exposed four strains of P. hermaphrodita (and DMG0001), three strains of P. neopapillosa and two strains of P. californica to mucus from seven common slug species. Furthermore, we investigated whether there was a relationship between chemoattraction and the numbers of offspring that were produced on each host species. Natural isolates of P. hermaphrodita differed in their preference of slug species whereas P. neopapillosa tended to prefer Arion sp. and strains of P. californica displayed striking differences in their responses. The reasons for positive chemoattraction to mucus were not due to higher numbers of offspring produced on these hosts.
Most studies on distribution of Phasmarhabditis spp. in slugs use dissection of individual slugs, which is time-consuming. Here we use a technique modified from that used to collect Pristionchus spp. ...nematodes from their beetle hosts. Slugs are decapitated and cadavers incubated for 1 week prior to examining for presence of adult nematodes. We compared the new technique with traditional dissection using field-collected untreated slugs, and slugs infected with Phasmarhabditis hermaphrodita in the laboratory. There was no difference in the efficacy of the two techniques. We also used the new technique to study prevalence of P. hermaphrodita at 22 New Zealand sites. We found P. hermaphrodita present at three sites and P. californica at two other sites suggesting Phasmarhabditis spp. are relatively common in New Zealand.
The grey garden slug (
), a common terrestrial slug native to Europe with a global distribution including North America, is commonly considered the most severe slug pest in agriculture. The nematode
..., which has been used in the U.K. and Europe as a commercial biocontrol agent since 1994, has also recently been collected in Oregon and California and has long been considered a candidate biocontrol agent for slug management in the U.S. In this study, we report differential gene expressions in nematode-infected slugs using RNA-seq to identify slug immune-related genes against nematodes. Comparison of gene expression levels between the whole bodies of a nematode-infected slug (N-S) and an uninfected control slug (C-S) revealed that there were a total of 39,380 regulated unigenes, of which 3084 (3%) were upregulated and 6761 (6%) were downregulated at greater than 2-fold change (FC > 2) in the nematode-infected slug. To further investigate the biological functions of differentially expressed genes (DEGs), gene ontology (GO) and functional enrichment analysis were performed to map the DEGs to terms in the GO, eukaryotic ortholog groups of proteins (KOG) and Kyoto Encyclopedia of Genes and Genome Pathway (KEGG) databases. Among these DEGs, approximately 228 genes associated with immunity or immune-related pathways were upregulated 2-fold or more in the N-S compared to C-S. These genes include toll, Imd, JNK, scavenger receptors (SCRs), C-type lectins (CTLs), immunoglobulin-like domains, and JAK/STAT63 signaling pathways. From the RNA-seq results, we selected 18 genes and confirmed their expression levels by qRT-PCR. Our findings provide insights into the immune response of slugs during nematode infection. These studies provide fundamental information that will be valuable for the development of new methods of pest slug control using pathogenic nematodes in the field.
Restrictions on the use of synthetic molluscicides highlight the importance of developing alternative control methods. Nevertheless, biocontrol agents can be costlier and less effective than ...synthetic counterparts. One means of increasing the efficacy of population suppression is to combine inundative biological control with habitat management to reduce population growth of target pests. Vineyards in the cool, wet climate of western England can suffer from outbreak densities of mollusc pests that damage expanding shoots, developing grapes and promote the transmission of fungal pathogens. In this study we combined the biocontrol agent Nemaslug - Phasmarhabditis hermaphrodita (Schneider) - with a simple habitat management approach (regular mowing) to suppress mollusc pests in vineyards in South Western England. Two sites were treated with NemaSlug and or mowing in a factorial design in early spring coinciding with bud burst and the start of mollusc growth and feeding. Mowing was effective management and resulted in the reduction of slug and snail populations and significantly less damaged vines. Nemaslug did not reduce slug numbers overall but did reduce bud damage, snail numbers and lowered the proportion of susceptible Deroceras spp in treated plots. However, effect sizes of nematode biocontrol were small, potentially because this product could not be applied to bare soil. Management practice for cool climate vineyards varies considerably from site to site. This study shows the value of simple habitat management for controlling a novel target and emphasises how consideration of pest biology can lead to effective alternatives.
The nematode Phasmarhabditis hermaphrodita is a lethal parasite of many pest slug and snail species. It is used as a commercial biological control agent (Nemaslug®) in Europe but a number of key ...gastropod pests (e.g. Lissachatina fulica) are thought to be unsusceptible. Our data, however, demonstrated that a recently discovered U.S. strain of P. hermaphrodita causes statistically significant mortality to neonate L. fulica and consequently this nematode could be an important IPM tool for managing this snail pest in areas where P. hermaphrodita has been discovered. Soil moisture content appears to play an important role in determining nematode efficacy.
The genetic mechanisms of how free-living nematodes evolved into parasites are unknown. Current genetic model nematodes (e.g. Caenorhabditis elegans) are not well suited to provide the answer, and ...mammalian parasites are expensive and logistically difficult to maintain. Here we propose the terrestrial gastropod parasite Phasmarhabditis hermaphrodita as a new alternative to study the evolution of parasitism, and outline the methodology of how to keep P. hermaphrodita in the lab for genetic experiments. We show that P. hermaphrodita (and several other Phasmarhabditis species) are easy to isolate and identify from slugs and snails from around the UK. We outline how to make isogenic lines using 'semi-natural' conditions to reduce in-lab evolution, and how to optimize growth using nematode growth media (NGM) agar and naturally isolated bacteria. We show that P. hermaphrodita is amenable to forward genetics and that unc and sma mutants can be generated using formaldehyde mutagenesis. We also detail the procedures needed to carry out genetic crosses. Furthermore, we show natural variation within our Phasmarhabditis collection, with isolates displaying differences in survival when exposed to high temperatures and pH, which facilitates micro and macro evolutionary studies. In summary, we believe that this genetically amenable parasite that shares many attributes with C. elegans as well as being in Clade 5, which contains many animal, plant and arthropod parasites, could be an excellent model to understand the genetic basis of parasitism in the Nematoda.
•Previous research has shown slugs avoid the nematode Phasmarhabditis hermaphrodita.•In contrast, slugs infected with P. hermaphrodita are attracted to the nematode•Uninfected slugs fed sertraline ...were attracted to P. hermaphrodita.•Slugs infected with P. hermaphrodita fed haloperidol were not attracted to nematodes.•Biogenic amines produce similar behavioural phenotypes as P. hermaphrodita infection.
The nematode Phasmarhabditis hermaphrodita can infect and kill many species of slugs and has been formulated into a biological control agent for farmers and gardeners. P. hermaphrodita can manipulate the behaviour of slugs, making those infected move to areas where the nematode is present. Research suggests P. hermaphrodita uses manipulation of biogenic amines to achieve this, however the exact role of serotonin and dopamine needs further elucidation. Here we fed slugs Deroceras invadens (uninfected and infected with P. hermaphrodita) apomorphine, sertraline and haloperidol and observed their behaviour when given a choice between a P. hermaphrodita infested habitat, or a parasite free area of soil. In contrast to their usual P. hermaphrodita avoidance behaviour, uninfected D. invadens fed sertraline were attracted to the nematodes and conversely those fed haloperidol avoided the nematodes. D. invadens fed apomorphine were recorded equally on the control and nematode side. D. invadens pre-infected with P. hermaphrodita fed sertraline and apomorphine were found significantly more on the side with the nematodes. However, suppressing dopaminergic signalling through feeding with haloperidol abrogated this attraction and slugs were found on both sides. These results demonstrate that serotonin and dopamine are potential regulators of behavioural manipulation by P. hermaphrodita.
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