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Repellent, antifeedant & molluscicidal effects of Commiphora spp. oleoresins, and their extracts, on Deroceras reticulatum and Helix aspersa

Ali, Ahmed 2005. Repellent, antifeedant & molluscicidal effects of Commiphora spp. oleoresins, and their extracts, on Deroceras reticulatum and Helix aspersa. PhD Thesis, Cardiff University.

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The oleoresin exudates from two species of Commiphora trees, and their extracts, were evaluated as novel methods of controlling terrestrial molluscs. Various test methods were employed including terraria trials, leaf disc assays, caged field trials and spray trials. Laboratory terraria trials with C. molmol (myrrh) and C. guidotti (opoponax) oleoresins, showed them to be effective repellent barriers against the terrestrial molluscs Deroceras reticulatum, Arion hortensis and Helix aspersa. Solid repellent barriers comprised of reduced amounts of myrrh oleoresin, mixed with inert materials (sawdust, corncob and sharp sand) and sawdust coated with extracts of myrrh and opoponax, were also very effective in repelling terrestrial molluscs. The botanical origin of myrrh and opoponax oleoresins were confirmed using gas chromatography-mass spectrometry (GC-MS) analytical techniques. The chemical compounds identified for myrrh were consistent with those reported for C. molmol, comprising mainly of sesquiterpenes and furano-sesquiterpenes, whilst the chemical compounds identified for opoponax were consistent with those reported for C. guidotti, comprising mainly of monoterpenes and sesquiterpenes. Comparison of the chemicals identified for commercial myrrh (Yemeni) and Somali myrrh (Guban) showed them both to contain the same bouquet of chemical compounds. Differences were observed in the gas chromatographic profile of Somali and Yemeni myrrh. Somali myrrh contained high levels of β-elemene, whilst Yemeni myrrh was dominated by the furano-sequiterpenes, curzerene and Furanoeudesma-1,3-diene. a-Santalene was the major sesquiterpene identified for the liquid extracts of opoponax, whilst /ra s-p-ocimene was the dominant chemical identified for the volatile odour associated with the opoponax oleoresin and its extracts. Leaf disc assays, with D. reticulatum slugs, confirmed the extracts of myrrh and opoponax, to be strong antifeedants at concentrations of 0.5% and 1% respectively. Both extracts significantly reduced the feeding behaviour of the slugs. A number of terpenoid chemicals were also evaluated, using the leaf disc assay, and showed significant antifeedant properties. The most potent of these chemicals was found to be /ra/ -p-ocimene, a major component of opoponax, and was found to possess both antifeedant and molluscicidal properties towards slugs. The molluscicidal nature of this monoterpene depended upon the polarity of the medium used to prepare it. Leaf discs assays with H. apersa snails, showed that higher concentrations of myrrh and opoponax extracts (3%) was required to deter the snails from feeding on the lettuce leaf discs. In addition higher concentration levels of rra s-p-ocimene (5%) was required to cause a similar antifeedant effect. In contrast to the slugs, no snail mortality was observed with these strong antifeedant extracts, however 100% snail mortality was observed after treating lettuce leaf discs with pure /rara'-p-ocimene oil. Emulsion stability was found to be dependent upon nature of the non-ionic surfactant incorporated into the formulation. Oil in water emulsions based on myrrh, opoponax and rra s-p-ocimene oils, containing 3 to 5% surfactant, were stable for time periods ranging from two weeks to more than 10 months. Emulsions based on Synperonic 91/8 were stable for two weeks, whilst those containing Tween 80 and Tween 20 were stable for approximately 10 months to one year. Caged field trials with repellent physical barriers comprised of 100% myrrh and opoponax oleoresins, reduced myrrh oleoresin mixed with inert substrates, and sawdust treated with ethanol and essential oil extracts of myrrh, all showed significant repellency properties towards D. reticulatum slugs for 14 days. Spray trials with myrrh, opoponax and rnms-p-ocimene, under controlled temperature conditions, showed them to be very effective in deterring slugs and snails from consuming lettuce plants. Myrrh essential oil and /raws-P-ocimene were also molluscicidal against the small field slug. Little slug mortality was observed when ethanol extracts of myrrh were employed, whilst still maintaining its strong repellent properties. No incidences of snail mortalities were observed throughout the spray trials. Myrrh and opoponax oleoresins were found to have no toxic effects on earthworms and their 3% extracts showed very little phytotoxic effects against lettuce plants. Traws-p-ocimene (5%) extracts were well tolerated but marginally affected one variety of curly lettuce. This study has shown the novel application of myrrh and opoponax oleoresins, their extracts, and their chemical components in affecting the feeding activity of terrestrial molluscs.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Biosciences
Subjects: Q Science > QK Botany
ISBN: 9781303203671
Date of First Compliant Deposit: 30 March 2016
Last Modified: 30 Jun 2022 12:37

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