TOXICITY OF IONIC THIOCYANATE-AMENDED SOIL TO THE WIREWORM LIMONIUS-CALIFORNICUS (COLEOPTERA, ELATERIDAE)

Glucosinolates contained in cruciferous plant tissues are hydrolyzed t o a variety of biologically active products that are potentially usefu l for control of soil-borne pests. Isothiocyanates have been shown to be toxic and repellent to wireworms, but little is known about the tox icity of another important glucosinolate degradation product, ionic th iocyanate (SCN-). This study reports on bioassays assessing acute and sublethal toxicity and repellency of soil amended with SCN- (supplied as KSCN) to the sugarbeet wireworm, Limonius californicus (Mannerheim) . Wireworms exposed to 0, 150, and 300 nmol SCN-/g soil for 7 d showed little mortality and no significant differences in mortality among tr eatment levels. There were no significant differences in mortality amo ng treatments for surviving wireworms maintained in untreated soil wit h germinating wheat seeds for an additional 35 d, suggesting no sublet hal effects from the initial 7-d exposure. An LC(50) of 12.36 X 10(4) nmol SCN-/g of soil, a concentration 600-fold greater than that genera ted from defatted Brassica napus L. (Brassicaceae) seed meal, was esti mated for wireworms exposed to SCN- for 24 h. Laboratory bioassays als o indicated that wireworms were not repelled by SCN--treated soil. Thu s, at concentrations generated from Brassica tissues, SCN- does not ap pear to play a major role in reducing wireworm populations.