Disruption of host-seeking behaviour by the salmon louse, Lepeophtheirus salmonis, using botanically derived repellents.

The potential for developing botanically derived natural products as novel feed-through repellents for disrupting settlement of the salmon louse, Lepeophtheirus salmonis (Caligidae) upon farmed Atlantic salmon, Salmo salar, was investigated using an established laboratory vertical Y-tube behavioural bioassay for assessing copepodid behaviour. Responses to artificial sea water conditioned with the odour of salmon, or to the known salmon-derived kairomone component, α-isophorone, in admixture with selected botanical materials previously known to interfere with invertebrate arthropod host location were recorded. Materials included oils extracted from garlic, Allium sativum (Amaryllidaceae), rosemary, Rosmarinus officinalis (Lamiaceae), lavender, Lavandula angustifolia (Lamiaceae), and bog myrtle, Myrica gale (Myricaceae), and individual components (diallyl sulphide and diallyl disulphide from garlic; allyl, propyl, butyl, 4-pentenyl and 2-phenylethyl isothiocyanate from plants in the Brassica genus). Removal of attraction to salmon-conditioned water (SCW) or α-isophorone was observed when listed materials were presented at extremely low parts per trillion (ppt), that is picograms per litre or 10-12 level. Significant masking of attraction to SCW was observed at a level of 10 ppt for diallyl disulphide and diallyl sulphide, and allyl isothiocyanate and butyl isothiocyanate. The potential of very low concentrations of masking compounds to disrupt Le. salmonis copepodid settlement on a host fish has been demonstrated in vitro.

Production of (5R,6S)-6-acetoxy-5-hexadecanolide, the mosquito oviposition pheromone, from the seed oil of the summer cypress plant, Kochia scoparia (Chenopodiaceae).

The oviposition pheromone for the pathogen-vectoring mosquitoes in the genus Culex (Diptera: Culicidae), that is, (5R, 6S)-6-acetoxy-5-hexadecanolide, is efficiently synthesized, in admixture with the inactive (5S,6R) enantiomer ( approximately 33% w/w), from the fixed oil extracted from the seeds of the summer cypress plant, Kochia scoparia (Chenopodiaceae), cultivated on an industrial scale. Oviposition bioassays using gravid females of Culex quinquefasciatus, a vector of filariasis in human beings, showed that the product was attractive, with activity comparable to that of a pure synthetic sample containing the same amount of the active enantiomer. Production of the pheromone in the form of a biologically active crude material via a cheap and renewable plant suitable for development as a new industrial crop provides the basis for control of Cx. quinquefasciatus and other congeneric vectors of pathogens in resource-poor areas of the world.