The role of time delays in a non-autonomous host–parasitoid model of slug biocontrol with nematodes

Thirty years of slug control using the parasitic nematode Phasmarhabditis hermaphrodita and beyond

Several slug species are highly pestiferous and threaten global sustainable agriculture. Current control methods rely heavily on metaldehyde pellets, which are often ineffective, harm nontarget organisms and have been banned in some countries. A viable alternative is the parasitic nematode Phasmarhabditis hermaphrodita (and recently P. californica), which has been formulated into a biological control agent (Nemaslug®) to control slugs across northern Europe. Nematodes are mixed with water and applied to soil where they seek out slugs, penetrate behind the mantle and kill them in 4-21 days. Phasmarhabditis hermaphrodita has been on the market since 1994 and since then there has been ample research on its use. Here we review the research carried out on P. hermaphrodita over the last 30 years since its development and release as a commercial product. We provide information on life cycle, worldwide distribution, history of commercialisation, gastropod immunity, host range, ecological and environmental factors that affect its success in the field, bacterial relationships, and summarise results of field trials. Finally, we suggest future directions for P. hermaphrodita research (and other Phasmarhabditis species) to enhance its use as a biological control agent to control slugs for the next 30 years. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

The ontogeny of host-seeking behaviour in a parasitoid dipteran

The robber fly Mallophora ruficauda is one of the principal apiculture pests in the Pampas region of Argentina. As adults, they prey on honeybees and other insects, while as larvae they are ectoparasitoids of third-instar scarab larvae. Females of M. ruficauda lay eggs in tall grasses. After being dispersed by the wind, larvae drop to the ground, where they dig in search of their hosts. It is known that M. ruficauda larvae exhibit active host-searching behaviour; however, it is unknown which instars are involved in this search. We carried out experiments in the laboratory to determine which larval stages are involved in host location. We report here that the second instar of M. ruficauda orientates specifically toward a source of Cyclocephala signaticollis odour, while first larval instar is indifferent to the host cues. Furthermore, we have determined that second instar larvae are more motivated to initiate exploratory movements than larva of the first stage. So far as we know, this is the first case among parasitoids, where the second instar is responsible for host location. Here we provide relevant information of this parasitoid's host-searching strategy, increasing the available knowledge of this significant apiculture pest.

Biological control of terrestrial molluscs using Phasmarhabditis hermaphrodita--progress and prospects

Phasmarhabditis hermaphrodita Schneider (Nematoda: Rhabditidae) is a nematode that parasitises a wide range of slug and snail species. It has been formulated into a biological control agent (Nemaslug) and was commercialised in 1994. It is now available in fourteen European countries. A review is given of all research on P. hermaphrodita, including basic biology, mass cultivation, formulation, host range, application strategies, field efficacy and effects on non-target organisms. The many critical gaps in present knowledge are highlighted, and future research is proposed that will lead to greater understanding of this unusual parasite and may enable its more widespread use in the management of mollusc pests.