Toxicity of Ionic Thiocyanate-Amended Soil to the Wireworm Limonius californicus (Coleoptera: Elateridae)

Abstract

Glucosinolates contained in cruciferous plant tissues are hydrolyzed to a variety of biologically active products that are potentially useful for control of soil-borne pests. Isothiocyanates have been shown to be toxic and repellent to wire worms, but little is known about the toxicity of another important glucosinolate degradation product, ionic thiocyanate (SCN). This study reports on bioassays assessing acute and sublethal toxicity and repellency of soil amended with SCN- (supplied as KSCN) to the sugar beet wire worm, Limonius californicus (Mannerheim). Wire worms exposed to 0, 150, and 300 nmol SCN-/g soil for 7 d showed little mortality and no significant differences in mortality among treatment levels. There were no significant differences in mortality among treatments for surviving wire worms maintained in untreated soil with germinating wheat seeds for an additional 35 d, suggesting no sublethal effects from the initial 7-d exposure. An LC50 of 12.36 × 104 nmol SCN-/g of soil, a concentration 600-fold greater than that generated from defatted Brassica napus L. (Brassicaceae) seed meal, was estimated for wire worms exposed to SCN- for 24 h. Laboratory bioassays also indicated that wire worms were not repelled by SCN -treated soil. Thus, at concentrations generated from Brassica tissues, SCN- does not appear to play a major role in reducing wire worm populations.