Toxicity of essential oils to slug parasitic and entomopathogenic nematodes

Abstract

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.

Allelopathic, Phytotoxic, and Insecticidal Effects of Thymus proximus Serg. Essential Oil and Its Major Constituents

“…Natural products with plant origin can play crucial roles in pest management practice (Faraone et al, 2015 ; Barua et al, 2020 ; Basaid et al, 2020 ; Chen and Oi, 2020 ). Previously, EOs synthesized by Thymus species have been demonstrated to possess insecticidal activity.…”

A Literature Review of Biological and Bio-Rational Control Strategies for Slugs: Current Research and Future Prospects

“…In the UK, it was isolated from the mantle cavity of an infected slug D. reticulatum in 1987 [17]. P. hermaphrodita is a soil-dwelling facultative mollusc-parasitic nematode that can complete its life on dead invertebrates and decaying leaf litter [29,30]. P. hermaphrodita dauer juvenile larvae infect molluscs by entering through natural openings and then developing to the adult stage and subsequently reproducing.…”

“…As an alternative to synthetic chemicals, plant-derived essential oils (EOs) are increasingly being used as biorational products in agriculture. Various scholars [30,[106][107][108][109] have argued that essential oils show antimicrobial, acaricidal, insecticidal, molluscicidal and nematicidal properties while demonstrating little or no toxicity to humans and the surrounding environment. The molluscicidal properties of essential oils have been mostly confirmed against terrestrial molluscs [110].…”

“…However, due to their nematicidal and insecticidal properties, the use of essential oils could be harmful to beneficial nematodes and insects. In fact, Barua [30] found that the following essential oils: thyme, cinnamon, clove, garlic, pine and lemongrass, cause mortality in the beneficial nematode species P. hermaphrodita, Steinernema feltiae and Heterorhabditis bacteriophora. In addition to essential oils, scientists have also shown interest in exploring other bio-rational products with slug control capabilities.…”

Biocontrol Activity of Aromatic and Medicinal Plants and Their Bioactive Components against Soil-Borne Pathogens

“…Although numerous cultural, physical, biological, and genetic options are available nowadays, the main strategies for controlling soil-borne pathogens are still highly dependent on the use of agrochemicals [ 15 , 21 ] due to their high efficiency and easy applicability [ 22 ]. Besides the positive effects, the indiscriminate use of these chemical agents may induce undesirable changes to the beneficial soil microorganisms and human and animal health [ 22 , 23 , 24 ]. The commonly applied chemical pesticides are usually effective against their target organisms, but they are not specific for them [ 25 ].…”