The role of semiochemicals in host location and non-host avoidance by salmon louse (Lepeophtheirus salmonis) copepodids

Abstract

The role and identity of host and non-host chemical cues (semiochemicals) in host location and non-host avoidance for copepodid larvae of sea lice, Lepeophtheirus salmonis, was investigated using Y-tube behavioural bioassays, solid-phase extraction (SPE), and coupled gas chromatography – mass spectrometry (GC–MS). Using artificial seawater conditioned with the preferred salmonid host, Salmo salar, L. salmonis displayed high activation and directional responses in Y-tube assays to salmon-conditioned water (SCW), to an extract of SCW prepared by SPE, and to a vacuum distillate of the SPE extract. Similar responses were observed to two chemicals identified from SCW by coupled GC–MS: isophorone and 6-methyl-5-hepten-2-one. Dose-response studies with isophorone showed that copepodid responses across the range tested were maximised at 0.01 and 0.1 mg·mL–1. A mixture of isophorone and 6-methyl-5-hepten-2-one also induced high activation and directional responses. Semiochemicals were also isolated from the non-host fish, turbot (Scophthalmus maximus (Rafinesque)), by SPE and analysed by GC–MS. Two non-host-specific chemicals were identified as 2-aminoacetophenone and 4-methylquinazoline. When SCW was mixed with either of the non-host chemicals, activation and directional responses to SCW were eliminated in the Y tube.

Chemoreception in the salmon louse Lepeophtheirus salmonis: an electrophysiology approach

“…L. salmonis can detect a range of environmental and host-related stimuli, e.g. pressure/moving water, light, salinity, temperature and semiochemicals (Wootten et al 1982, Bron et al 1993, Heuch & Karlsen 1997, Devine et al 2000, Ingvarsdóttir et al 2002a,b, Luntz 2003, Beamish et al 2005, Bailey et al 2006. Visual cues, such as a decrease in light intensity resulting from shadows of fish swimming overhead, would operate at long range, i.e.…”

“…Fields & Yen 2002, Yen & Okubo 2002) associated with an individual fish may provide directional signals that allow the louse to accurately leap towards a specific host. This also appears to be true for salmon lice copepodids and adults, which are attracted to strong chemical sources emanating from a y-maze (Ingvarsdóttir et al 2002a, Bailey et al 2006 or for the response of copepodids to fluid mechanical signals created by a moving silicone cast of a salmon head (Heuch et al 2007). At this scale, it is critical that L. salmonis is able to perform an accurately directed leap towards a potential host.…”

Courtship behavior and potential indications for chemical communication in Artemia franciscana (Kellog 1906)

“…SOLID PHASE EXTRACTION (SPE) AND VACUUM DISTILLATION SPE was performed for the adsorption of the semiochemicals present in CW and CCW following the protocols reported by Ingvarsdottir et al (2002aIngvarsdottir et al ( , 2002b, Bailey et al (2006) and Pino-Marambio et al (2007). Trapping columns (Biotage, Uppsala -Sweden) consisted of 6 mL glass cartridges containing two layers (C2 (500 mg) over ENV + (200 mg)).…”

“…This technique allowed the separation of the non-polar and polar fractions. This process yielded an ethanolic distillate containing non-polar chemical compounds and a residue constituted mainly of polar components (Pickett & Griffi ths 1980;Ingvarsdottir et al 2002aIngvarsdottir et al , 2002bBailey et al 2006). The residue was then dissolved with 1 mL of ethanol (HPLC grade, Darmstadt -Germany) and 1 mL of water (HPLC grade, Darmstadt -Germany).…”

DEET repels ORNery mosquitoes

“…In addition, some insects apparently can still detect the host by means of a highly sensitive and selective olfactory-based host-location capability. More recently, successful attempts have been made to identify experimental repellents derived from species closely related to the host range but not naturally acting as hosts (6,7). There is also considerable promise in repellents active against the malaria mosquito (An.…”