Trends in arthropod defensive secretions, an aquatic predator assay

Twenty-five arthropod defensive chemicals were tested on a potential fish predator to assay basic repellency, interniche effectiveness and mimetic interactions among repellents, and predator tolerance to repellents.The defensive secretions of aquatic arthropods are more effective repellents than those of terrestrial or cryptozoic arthropods. Phenolic compounds are more effective than carbonylic or acidic compounds. Repellency is most effective in compounds of reduced water solubility. Repeated exposure to gradually increasing molar concentrations of benzoic acid resulted in a greater acceptability of this compound to fish predators. It is suggested that Mullerian mimicry systems based on large numbers of species may be susceptible to dilution effects in terms of effectiveness.