Essential oils are being increasingly utilised as a biorational element in integrated pest management regimes. Whereas there has been much research on the effects of these oils on mortality and ...behaviour of pestiferous molluscs, insects and nematodes, there has (to the present authors’ knowledge) been no research into their effects on the mortality and behaviour of beneficial nematodes. We address this lacuna by conducting laboratory assays on the behaviour (thrashing assays) and mortality of 13 essential oils plus controls of Tween and water on the malacophagous nematode
Phasmarhabditis hermaphrodita
and two species of entomopathogenic nematodes, namely:
Steinernema feltiae
and
Heterorhabditis bacteriophora
. Mortality results showed an “all or nothing” response with only three oils—pine oil, peppermint and lemongrass—displaying intermediate mortalities. Also, toxicity of essential oils was conserved across phylogenetically quite distinct beneficial nematode species with oil toxicity largely being repeated across the three beneficial nematodes. Thrashing assays confirmed the toxic effects of certain oils. We recommend that the effects of essential oils be tested on beneficial organisms in ecosystems before choices are made over which oils should be used. The present paper highlights some oils which are not toxic to beneficial nematodes but may affect their behaviour. Research should focus on these oils as part of a biorational control programme for pestiferous molluscs and insects.
Several slug species are voracious pests of agricultural crops in northern Europe and are difficult to control. The parasitic nematode Phasmarhabditis hermaphrodita has been developed as a slug ...control product, but there is little information about whether it could be combined with other control methods (such as essential oils) to enhance its efficacy. Here, we carried out experiments in propagators with lettuce at three different time periods (July, September and October), and tested the following treatments: water (untreated control), cedarwood oil, P. hermaphrodita, cedarwood oil and P. hermaphrodita, and Tween 80 (used as an emulsifier for the cedarwood oil solution). Lettuce was grown in propagators with either 10 Deroceras reticulatum or 5 Arion vulgaris and the percentage of lettuce eaten over 14 days (as well as weight, the number of live slugs and eggs produced) was recorded. Cedarwood oil reduced slug damage, slug numbers and slug eggs in the experiments with D. reticulatum, and P. hermaphrodita performed well in two out of three experiments. The mixture of P. hermaphrodita and cedarwood oil was superior in reducing the proportion of lettuce eaten compared to single doses of each treatment in one out of three trials. In propagators with A. vulgaris all treatments performed poorly. In summary, P. hermaphrodita and/or cedarwood can be used to reduce damage by D. reticulatum, but are ineffective at controlling A. vulgaris. Slugs from the genus Arion continue to be a difficult group to control.
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•Slugs are prolific agricultural pests and are difficult to control.•Novel slug control methods are needed.•Parasitic nematodes and cedarwood oil were combined for optimised slug control.•A combined effect on slug control was observed in one out of three trials.•Cedarwood oil is a promising slug control method.
Pestiferous slugs pose a significant global threat to sustainable agriculture, horticulture and floriculture (Barker, 2002). Slugs cause crop damage by eating seeds, stems, growing points and leaves, ...leading to a reduction in growth (Port, 1986; South, 1992). They can be a major pest throughout the lifecycle of field vegetables and in extreme cases, whole fields have to be re-sown resulting in economic losses (Willis et al., 2006). Contamination of the harvested crop also occurs from slug mucus and faeces, resulting in poor product quality (Port and Ester, 2002). It is estimated that a lack of slug control for crops such as oilseed rape and wheat would lead to £43.5 million a year in loss of product in the UK alone (Nicholls, 2014). In Europe, wheat and oilseed rape suffer greatly from slug damage (Ester and Wilson, 2005) and in 2010 it was reported that 22% of winter wheat crops suffered damage from slugs, and if left untreated by chemical molluscicides a 5% decrease in yield would be expected (ADAS, 2010). As well as causing damage in agriculture, slug feeding can affect plant community diversity and richness (Wilby and Brown, 2001) with preferential feeding on native species aiding in exotic plant growth (Joe and Daehler, 2008). Slug feeding reduces conservation efforts such as forest regeneration (Côté et al., 2005) and threatens endangered species such as lichens (Cameron, 2009). Slugs can also act as invasive pests, causing damage to native plants that may not have anti-herbivore defences due to limited predation pressure (Feeny, 1992) and alter species composition (Schreiner, 1997). Slugs can also be responsible for transmitting plant pathogens (Wester et al., 1964; Hasan and Vago, 1966) including Phytophthora (Telfer, 2015). They can also act as vectors of nematode parasites (South, 1992; Grewal et al, 2003a), such as the rat lungworm, Angiostrongylus cantonensis, the causal agent of eosinophilic meningitis, which is recognised as an emerging tropic and sub tropic zoonotic disease (Yong et al., 2015). Other veterinary important nematode parasites vectored by slugs include Angiostrongylus vasorum, Muellerius capillaris and Protostrongylus tauricus (Patel et al., 2014; Lange et al., 2018).Slugs are commonly controlled by chemical bait pellets containing metaldehyde. In the past methiocarb was used, however it is toxic to beneficial invertebrates and other nontarget organisms (Purvis and Bannon, 1992; Nicholls, 2014).The use of Metaldehyde in Great Britain was banned from the 1st April 2022 ( Jones, 2022). Metaldehyde pellets were used globally (Castle et al., 2017). From 2008 to 2014 an estimated 1640 t of metaldehyde was used in the UK alone (Simms et al., 2006). Slugs feed on the pellets and exhibit symptoms such as increased levels of mucus secretion and paralysis, and die within several days from water loss (Booze and Oehme, 1986; Bailey, 2002). Though effective these bait pellets also cause harm to non-target organisms including canines and other vertebrates (Cope et al., 2006). Metaldehyde is also now considered an important emerging pollutant of concern due to leaching into watercourses (Stuartet al., 2012) as it is highly mobile in soil (Kay and Grayson, 2014). Furthermore, in parts of the UK metaldehyde concentrations in water bodies have exceeded the European Union’s regulatory drinking water standard for pesticides (Kay and Grayson, 2014). An alternative slug pellet (Ferramol®) is composed of iron III phosphate or ferric phosphate and is registered for use in many European countries (Speiser and Kistler, 2001). It has been used to control slugs e.g.Arion ater, however it has been shown that high doses can lead to mortality and reduced activity in earthworms (Langan and Shaw, 2006).
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