Advantageous attributes of larval whitefringed weevil, Naupactus leucoloma(Coleoptera : Curculionidae) for bioassaying soil fumigants, and responsesto pure and plant-derived isothiocyanates

First instars of the soil-inhabiting whitefringed weevil, Naupactus leucolo ma (Boheman), are a particularly good bioassay model for assessing volatile soil fumigants and biofumigants. Eggs are readily obtained and can be stor ed for long periods with larvae hatched on demand and the first instar is n on-feeding, surviving without food or shelter. Longevity varies with temper ature, but readily accommodates the period required to conduct bioassays wi thout appreciable mortality of untreated controls. In vitro bioassays of pu re methyl isothiocyanate, the active ingredient from metham sodium soil fum igant, and the less volatile 2-phenylethyl isothiocyanate, sensitively dete cted differences in toxicity and effects of temperature. Bioassay of volati les emitted from hydrolysed tissue of various isothiocyanate-producing Bras sica plants revealed widely varying toxicity effects, indicating that bioas says with N. leucoloma are a sensitive and relevant indicator of the potent ial of different plants for biofumigation of soil-borne pest organisms.