Louise Hughes

Laboratory tests of the potential of entomopathogenic nematodes for the control of field slugs (Deroceras reticulatum)

The entomopathogenic nematodes, Steinernema feltiae (UK 76) and Heterorhabditis sp. (North West European Group, UK 211), and the slug-parasitic nematode Phasmarhabditis hermaphrodita (UK 1) were tested for their ability to kill the slug Deroceras reticulatum using petri dish and soil bioassays. The entomopathogenic nematodes did not kill slugs in either bioassay at 14 and 23°C, although they were shown to kill tenebrionid insect larvae (Tenebrio molitor and Zophobas morio) at 14°C. The symbiotic bacteria of S. feltiae and Heterorhabditis sp. (Xenorhabdus bouienii and Photorhabdus luminescens, respectively) were injected in large numbers into the hemocoel of D. reticulatum. X. bovienii was found to be of low pathogenicity and P. luminescens was not pathogenic, whereas slugs were rapidly killed by injection of a strain of Pseudomonas fluorescens isolated from a cadaver of D. reticulatum. P. hermaphrodita killed D. reticulatum at 14°C but not at 23°C and did not kill T. molitor or Z. morio at 14°C. It is concluded that S. feltiae and Heterohabditis sp. have no potential as biocontrol agents against slugs, whereas P. hermaphrodita is effective at the relatively low temperatures at which slugs are active.

Effects of Phasmarhabditis hermaphrodita on non-target molluscs

Two field experiments were done in which plots of oilseed rape, immediately adjacent to the field margin, were left untreated or treated with the slug-parasitic rhabditid nematode Phasmarhabditis hermaphrodita. Nematodes were applied at a rate of 3 × 10 9 ha -1 . Slug populations within plots were low and nematode application had little detectable effect on slug numbers, biomass or slug damage to the crop. There was a large snail community in the field margin in both experiments, but P hermaphrodita had no detectable effect on the abundance of any of the nine snail species recorded. The susceptibility of seven common hedgerow species (Monacha cantiana, Cepaea hortensis, Cepaea nemoralis, Pomatias elegans, Oxychilus helveticus, Clausilia bidentata and Discus rotundatus) to P hermaphrodita was tested in the laboratory. Snails were kept confined for three weeks on soil without nematodes, or with P hermaphrodita applied at the recommended application rate or five times this rate. Soil treatment with the recommended rate of nematodes caused significant mortality only for the snail M cantiana and the susceptible slug Deroceras reticulatum. Soil treatment with five times the recommended rate caused significant mortality of the slug D reticulatum and the snails M cantiana and C hortensis, but not any other species. Reasons why application of P. hermaphrodita to arable crops in Britain is unlikely to pose a substantial threat to non-target molluscs are discussed.

The comparative immunology of wild and laboratory mice, Mus musculus domesticus.

The laboratory mouse is the workhorse of immunology, used as a model of mammalian immune function, but how well immune responses of laboratory mice reflect those of free-living animals is unknown. Here we comprehensively characterize serological, cellular and functional immune parameters of wild mice and compare them with laboratory mice, finding that wild mouse cellular immune systems are, comparatively, in a highly activated (primed) state. Associations between immune parameters and infection suggest that high level pathogen exposure drives this activation. Moreover, wild mice have a population of highly activated myeloid cells not present in laboratory mice. By contrast, in vitro cytokine responses to pathogen-associated ligands are generally lower in cells from wild mice, probably reflecting the importance of maintaining immune homeostasis in the face of intense antigenic challenge in the wild. These data provide a comprehensive basis for validating (or not) laboratory mice as a useful and relevant immunological model system.

Genes important in the parasitic life of the nematode Strongyloides ratti

Parasitic nematodes are important pathogens of humans and other animals. The genus Strongyloides has both a parasitic and a free-living adult generation. S. ratti infections of its rat host are negatively affected by the host immune response, such that a month after infection, worms are lost from the hosts. Here we have investigated the changes in parasite gene expression that occur as the anti-S. ratti immune pressure increases. Existing S. ratti expressed sequence tags were used to construct a microarray consisting of 2227 putative genes. This was probed with cDNA prepared from parasites subject to low or high immune pressures. There are significant changes in the gene expression of S. ratti when subject to different immune pressures. Most of the genes whose expression changes have no significant alignment to known genes. These data together with previous S. ratti EST data were then used to identify genes that we hypothesise are central to the parasitic life of S. ratti and, perhaps, other parasitic nematodes. These analyses have identified genes likely to play a key role in the parasitic life of S. ratti; these genes should be the priority for further investigation.

A microarray analysis of gene expression in the free-living stages of the parasitic nematode Strongyloides ratti

BackgroundThe nematode Strongyloides ratti has two adult phases in its lifecycle: one obligate, female and parasitic and one facultative, dioecious and free-living. The molecular control of the development of this free-living generation remains to be elucidated.ResultsWe have constructed an S. ratti cDNA microarray and used it to interrogate changes in gene expression during the free-living phase of the S. ratti life-cycle. We have found very extensive differences in gene expression between first-stage larvae (L1) passed in faeces and infective L3s preparing to infect hosts. In L1 stages there was comparatively greater expression of genes involved in growth. We have also compared gene expression in L2 stages destined to develop directly into infective L3s with those destined to develop indirectly into free-living adults. This revealed relatively small differences in gene expression. We find little evidence for the conservation of transcription profiles between S. ratti and S. stercoralis or C. elegans.ConclusionThis is the first multi-gene study of gene expression in S. ratti. This has shown that robust data can be generated, with consistent measures of expression within computationally determined clusters and contigs. We find inconsistencies between EST representation data and microarray hybridization data in the identification of genes with stage-specific expression and highly expressed genes. Many of the genes whose expression is significantly different between L1 and iL3s stages are unknown beyond alignments to predicted genes. This highlights the forthcoming challenge in actually determining the role of these genes in the life of S. ratti.