Toxicity of isothiocyanates produced by glucosinolates in brassicaceae species to black ville weevil eggs

Control of the black vine weevil, Otiorhynchus sulcatus (F.), with allelochemicals produced from glucosinolates may be possible; however, plant-derived isothiocyanates are not readily available for bioassays. Our objective was to predict the toxicity of plant-derived isothiocyanates using a model developed with commercially available compounds. Contact toxicities of 12 organic isothiocyanates were determined by dipping black vine weevil eggs into isothiocyanate solutions. Quantitative relationships between the molecular structure of the isothiocyanates and their toxicities were estimated by regressing lethal concentrations against the compound's respective physiochemical parameters. Isothiocyanate polarity (log octanol/water partition coefficient) had the most significant effect on observed toxicities, whereas electronic and steric characteristics were unimportant. Using this linear structure-activity relationship, we predict that the highest contact toxicities to black vine weevil eggs will result from glucosinolates producing isothiocyanates with higher numbers of carbon atoms or those bearing sulfinyl, thio, or aromatic moieties.