Ex vivo development of Phasmarhabditis spp. associated with terrestrial molluscs

The success of Phasmarhabditis hermaphrodita (Schneider) Andrássy (Rhabditida: Rhabditidae) as a biological control agent of molluscs has led to a worldwide interest in phasmarhabditids. However, scant information is available on the lifecycle development of species within the genus. In the current study, the development of P. hermaphrodita, Phasmarhabditis papillosa, Phasmarhabditis bohemica and Phasmarhabditis kenyaensis were studied using ex vivo cultures, in order to improve our understanding of their biology. Infective juveniles (IJs) of each species were added to 1 g of defrosted homogenized slug cadavers of Deroceras invadens and the development monitored after inoculated IJ recovery, over a period of eight–ten days. The results demonstrated that P. bohemica had the shortest development cycle and that it was able to produce first-generation IJs after eight days, while P. hermaphrodita, P. papillosa and P. kenyaensis took ten days to form a new cohort of IJs. However, from the perspective of mass rearing, P. hermaphrodita has an advantage over the other species in that it is capable of forming self-fertilizing hermaphrodites, whereas both males and females are required for the reproduction of P. papillosa, P. bohemica and P. kenyaensis. The results of the study contribute to the knowledge of the biology of the genus and will help to establish the in vitro liquid cultures of different species of the genus.

Natural variation in host-finding behaviour of gastropod parasitic nematodes (Phasmarhabditis spp.) exposed to host-associated cues

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.

Genetic evidence illuminates the origin and global spread of the slug Deroceras invadens

ABSTRACT The terrestrial slug Deroceras invadens has spread across much of the world over the last century. What is there to learn about its origin, colonizations and diversity by comparing barcoding sequences of the mitochondrial gene COI (cytochrome c oxidase subunit I)? Samples from 317 localities covering most of the species’ range yielded 87 haplotypes. Higher diversity, the predominance of private haplotypes and geographic structuring all indicate a native range centred on southern Italy, including eastern Sicily. In contrast, central Italy is dominated by one haplotype, although accompanied by both close and more distant relatives; the lack of geographic structuring suggests recent expansion from a restricted distribution within that region. Beyond the Alps, two haplotypes predominate, accompanied by very similar variants; such star-shaped genealogies characterize recent population growth. Also, some rarer haplotypes have been independently introduced. Generally, haplotypes are well mixed here, often co-occurring at a locality. In North America and Australasia, some frequent haplotypes were likely directly introduced from Italy, because they were not found elsewhere in Europe. The rarity or absence in these continents of one or other of the two dominant European haplotypes suggests that import inspections have restricted repeated introductions. A skyline plot detects the recent demographic expansion but also indicates an earlier population decline in the native area. This may explain why the one-dimensional summary statistics FS and R2 did not signal population growth. A review of 41 other studies that used DNA to analyse invasions of terrestrial molluscs documents considerable diversity in methodology. Studies using genetic data to date recent invasions probably should adjust standard substitution rates upwards.

Slug Monitoring and Impacts on the Ground Beetle Community in the Frame of Sustainable Pest Control in Conventional and Conservation Agroecosystems

In conservation agriculture, slugs are considered significant pests and their monitoring is a key option in the integrated pest management framework. Together with molluscicide applications, predators such as ground beetles can offer a tool for slug control in the field. Through the evaluation of slug and ground beetle monitoring strategies, this work compared their presence in conventional and conservation agricultural plots. The invasive Deroceras invadens was the dominant slug species to occur in all sampling periods. Among Carabidae, Poecilus cupreus and Pterostichus melas were the most abundant species, and Bembidion spp., Brachinus spp., and Harpalus spp. were also common. Beer-baited pitfall traps, whatever their alcoholic content, caught more slugs and ground beetles than wooden boards used as shelters. Slugs were more abundant in conventional plots than in conservation plots, possibly due to the lower presence of natural enemies such as ground beetles. Despite possible impacts on Carabidae, beer-baited pitfall traps should be considered a useful tool for slug monitoring and for the planning of molluscicide applications. Soil management such as minimum- or no-tillage and the presence of cover crops are important elements influencing both slug and ground beetle presence, possibly playing a key role in the maintenance of natural enemy populations.

THE FIRST RECORD OF DEROCERAS INVADENS (GASTROPODA: PULMONATA: AGRIOLIMACIDAE) FOR MONTENEGRO

This article gives the first record of Deroceras invadens (Gastropoda: Pulmonata: Agriolimacidae) for Montenegro.