Michael J. Wilson

Entomopathogenic nematode foraging strategies – is Steinernema carpocapsae really an ambush forager?

For many years, entomopathogenic nematodes have been classified as either ‘ambush’, ‘cruise’ or ‘intermediate’ foragers. Here, we critically examine the evidence that Steinernema carpocapsae, the most studied ‘ambush’ forager, does actually use an ambush foraging strategy in nature. We propose an alternative hypothesis for the characteristic behaviours of S. carpocapsae (and other supposed ‘ambush’ foragers) based on adaptation to habitats other than mineral soils in which S. carpocapsae can ‘cruise’. Several papers are reviewed in which S. carpocapsae was used successfully to control sedentary or cryptic pests in organic habitats, thus supporting our hypothesis. If this hypothesis is correct, it does not preclude S. carpocapsae (or any entomopathogenic nematode species) using an ambushing strategy under certain circumstances, but we believe on current evidence that the classification of S. carpocapsae as an ambush forager cannot be sustained.

Slugs: Potential Novel Vectors of Escherichia coli O157

ABSTRACT Field and laboratory studies were performed to determine whether slugs could act as novel vectors for pathogen (e.g., Escherichia coli O157) transfer from animal feces to salad vegetables. Escherichia coli O157 was isolated from 0.21% of field slugs from an Aberdeenshire sheep farm. These isolates carried the verocytotoxin genes (vt1 and vt2) and the attaching and effacing gene (eae), suggesting that they are potentially pathogenic to humans. Strain typing using multilocus variable number tandem repeats analysis showed that slug and sheep isolates were indistinguishable. Laboratory experiments using an E. coli mutant resistant to nalidixic acid showed that the ubiquitous slug species Deroceras reticulatum could carry viable E. coli on its external surface for up to 14 days. Slugs that had been fed E. coli shed viable bacteria in their feces with numbers showing a short but statistically significant linear log decline. Further, it was found that E. coli persisted for up to 3 weeks in excreted slug feces, and hence, we conclude that slugs have the potential to act as novel vectors of E. coli O157.

Temporal Variation and Host Association in the Campylobacter Population in a Longitudinal Ruminant Farm Study

ABSTRACT Campylobacter jejuni and C. coli were quantified and typed, using multilocus sequence typing (MLST), from fecal samples collected from a mixed cattle and sheep farm during summer. Cattle had a significantly higher prevalence than sheep (21.9% [74/338] and 14.0% [30/214], respectively), but both decreased over time. There were no differences in the average Campylobacter concentrations shed by cattle (600 CFU g−1) and sheep (820 CFU g−1), although sheep did show a significant temporal reduction in the number of Campylobacter organisms shed in their feces. A total of 21 different sequence types (STs) (97.7% C. jejuni, 2.3% C. coli) were isolated from cattle, and 9 different STs were isolated from sheep (40.6% C. jejuni, 59.4% C. coli). The Campylobacter population in cattle was relatively stable, and the frequencies of genotypes isolated showed little temporal variation. However, the composition of subtypes isolated from sheep did show significant temporal differences. The cattle and sheep consistently showed significant differences in their carriage of Campylobacter species, STs, and CCs despite the fact that both were exposed to the same farming environment. This work has highlighted the patterns of a Campylobacter population on a ruminant farm by identifying the existence of both temporal and between-host variations.

Progress in the commercialisation of bionematicides

In the last few years, there have been numerous developments in the commercialisation of bionematicides. Here we briefly review the commercial status of four key active ingredients backed by large international companies and which are, or are likely to become widely available soon. We also identify research priorities. While scientists have intensively researched Pasteuria spp. and Purpureocillium lilacinus as potential nematicides, little research has been done on Bacillus firmus and Myrothecium verrucaria fermentation products. Conversely, a survey of the trade press suggests that these latter two agents, particularly B. firmus, are the most widely used. There is a clear need to further understand the ecology and mode of action of B. firmus when used as a bionematicide. Furthermore, while all active ingredients have proven efficacy in laboratory and/or small plot trials, there is a paucity of independent data showing product efficacy in target markets.

Pathogens and parasites of terrestrial molluscs

Compared with insect pathology, the pathology of terrestrial molluscs is in its infancy. There are no known viral or fungal pathogens of slugs or snails and knowledge of their bacterial pathogens is rudimentary and often anecdotal. More is known about microsprodia and protozoan parasites, and most work has concentrated on nematode parasites. One nematode parasite, Phasmarhabditis hermaphrodita , has been commercialized as a biological molluscicide and is sold in many European countries. In this chapter techniques for working with slugs and snails are described, as are handling techniques developed specifically for all groups of known molluscan pathogens and parasites.

Testing a new low-labour method for detecting the presence of Phasmarhabditis spp. in slugs in New Zealand

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.

Born to be Wild – Don’t Forget the Invertebrates

Parasitology research mostly aims to control parasites of humans and domesticated animals. Recently, many scientists have realized much can be learned by studying wildlife parasites. To this end, Trends in Parasitology published two special issues comprising some of the most interesting, topical science relating to wildlife parasitology [1]. The emphasis of the published articles was almost exclusively on parasites that use vertebrate animal hosts. Here, we argue that progress in parasitology could be accelerated if more parasitologists studied parasites that use invertebrates as definitive hosts.

Phasmarhabditis hermaphrodita as a Control Agent for Slugs

While there has been intense study on entomopathogenic nematodes (EPNs) by numerous research groups throughout the world, there has been much less work on nematodes that can control slugs. A survey of academic research papers listed in the Scopus database in December 2014 using the search terms “Steinernema or Heterorhabditis” revealed over 2,100 hits compared with a mere 82 hits for “Phasmarhabditis”. Conversely, while the EPNs have a relatively recent history, with the first Steinernema spp. being described in 1923 (Steiner, 1923), Phasmarhabditis hermaphrodita Schneider (Rhabditida: Rhabditidae) was first described as a parasite of slugs in 1859 (Schneider, 1859). The slug parasitic nematode, P. hermaphrodita featured prominently in Maupas’ classic paper on nematode reproduction (Maupas, 1900). This paper is best known for including the original description of Caenorhabditis elegans Maupas (Rhabditida: Rhabditidae) but the paper also contained drawings, measurements, and experimental observation on the reproduction of P. hermaphrodita which Maupas called Rhabditis caussaneli. However, there was virtually no more work done on this nematode until its potential for commercialisation as a bio–pesticide was first realised, and published as a patent (Wilson, Glen, & Pearce, 1993). The lifecycle of P. hermpahrodita is similar in many ways to EPNs (Table 21.1). The infective stage is a dauer larva that penetrates slugs through the dorsal integumental pouch (Wilson, Glen, & George, 1993; Tan & Grewal, 2001a). Larvae feeding within the slug develop into adults and eventually kill the host within 4–21 days. However, there are certain key differences from EPNs, most notably that P. hermaphrodita is a facultative parasite that can reproduce on a wide range of substrates including slug faeces, dead earthworms, dead insects, compost and leaf litter (Tan & Grewal, 2001a; MacMillan et al., 2009; Nermuť, Půža, & Mracek, 2014). But apart from this basic understanding, we have very little knowledge of the nematode’s biology and ecology.

Description and systematic affinity of Alaninema ngata n. sp. (Alaninematidae: Panagrolaimorpha) parasitising leaf-veined slugs (Athoracophoridae: Pulmonata) in New Zealand

A new Alaninema species associated with leaf-veined slugs (Athoracophoridae) in New Zealand is described and illustrated. Alaninema ngata n. sp. is characterised by a very long, cylindrical body, rounded head bearing two circles of cephalic papillae and amphids, shallow stoma with three bifid teeth, muscular, cylindroid pharynx lacking valves, enlarged, rounded cardia, nerve ring crossing the anterior intestine, excretory pore situated just posterior to nerve ring, monodelphic females with post-median vulva, thick-shelled eggs covered with prominent tubercles, monorchic males with short testis reflection, reduced number of male genital papillae, strong equal spicules and gubernaculum and tail tip bearing about 20 digitate processes. It is distinguished from A. venmansi and A. njoroensis by having a larger body size (mean 8.3 mm and 13.8 mm in males and females, respectively vs 8.2 mm females in A. venmansi and 4.8 mm and 5.5 mm in A. njoroensis males and females, respectively) and more anterior vulval position (V = 51.6 vs 70 and 66.4 in A. venmansi and A. njoroensis, respectively). Analyses of a partial 18S rDNA sequence indicate that A. ngata n. sp. is affiliated to the Panagrolaimorpha. The systematic position, host range and distribution of A. ngata n. sp. are discussed.

An improved bioassay for screening bacteria for biocontrol activity against slugs that avoids volatile-induced slug mortality

Abstract A strain of Stenotrophomonas maltophila previously thought to have molluscicidal activity was tested using a standard bioassay. Initial results on host range and dose response were promising. However, slug mortality was induced by volatile compounds released from the decaying food rather than by infection. We propose a modification of the bioassay that avoids this problem.