Cantharidin Levels in Blister Beetles (Coleoptera: Meloidae) Associated with Alfalfa in Colorado

Abstract

Livestock poisoning sometimes occurs when animals are fed alfalfa hay containing dead blister beetles. The toxin found in blister beetles, cantharidin, was measured in six species of Epicauta that feed on Colorado alfalfa, and compared with that of three blister beetles from other genera not usually associated with alfalfa. Significant differences in cantharidin concentrations were found among species. The most common blister beetles, Epicauta pennsylvanica (De Geer) and E. maculata (Say), had low (ca. 0.2 mg per beetle) and moderate (ca. 0.7 mg per beetle) levels of cantharidin, respectively. E. immaculata (Say), which was sporadically abundant in southeast Colorado, had high (ca. 4.8 mg per beetle) levels of cantharidin. Females had a significantly lower concentration (percentage of dry weight) of cantharidin. The number of beetles needed to induce mortality was estimated for horses of various weights ingesting beetles with various cantharidin levels.