Toxicity of Sorghum Roots to Larvae of the Western Corn Rootworm123

The roots of sorghum, Sorghum vulgare Pers., were found to he toxic to the larvae of Diabrotica virgifera LeConte. Preliminary tests suggested that the toxin involved was hydrocyanic acid. Other experiments showed that free cyanide was toxic to the larvae when it was ingested at a level of 10 ppm. Cyanogenetic glucosides were not toxic to larvae when ingested at a level equivalent to 2000 ppm cyanide unless appropriate hydrolytic enzymes were present. We suggest that toxic levels of hydrocyanic acid result during larval feeding on sorghum roots because of the action of a beta glucosidase on endogenous cyanogenetic glucosides such as dhurrin.