Cantharidin Content of Blister Beetles (Coleoptera: Meloidae) Collected from Kansas Alfalfa and Implications for Inducing Cantharidiasis

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Abstract
Cantharidin contents were determined for four Epicauta species abundant in northeast Kansas alfalfa fields. E. occidentalis (Werner) and E. pennsylvanica (DeGeer) typically contained much cantharidin (198–266 μ g/beetle), representing nearly 1% of their dry body weight, significantly more toxin than possessed by E. fabricii (LeConte) and E. pestifera Werner. Two species also exhibited significant intersexual differences in cantharidin content. E. occidentalis males had almost four times more cantharidin than females. In contrast, female E. pennsylvanica contained approximately six times as much of the substance as males. Three bales of alfalfa hay were collected from an area of a field infested with a swarm of E. occidentalis at the time of harvest. Blister beetles were recovered from 91% of the mechanically produced sections of compressed hay (commonly known as flakes) from these bales. Although the contamination in only one flake of hay approached a calculated lethal level of 25 mg/kg forage, these data indicate that an encounter with a single blister beetle-contaminated flake of hay in the toxic range is quite possible, albeit infrequent. Flakes of field-collected hay, contaminated at the highest observed levels, could provide a lethal dose of cantharidin to horses weighing 125–500 kg.

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