Factors Influencing Quantity of Cantharidin Transferred to Alfalfa from Epicauta occidentalis Werner (Coleoptera: Meloidae)

Abstract

Blister beetles, including Epicauta occidentalis Werner, contain cantharidin, which is a toxin that may cause severe irritation of the digestive tract and even death of livestock that ingest contaminated alfalfa. During harvest, alfalfa is easily contaminated by fluids and bodies of blister beetles, either by the crushing action of mechanical conditioning or by running over beetles with tractor tires when using sicklebar mowers for cutting. We developed a thin-layer chromatographic cleanup procedure followed by gas chromatographic analysis to quantify how cantharidin transfer to alfalfa is influenced by the condition and location of beetles in the crop. During the harvest process, living E. occidentalis located on top of cut alfalfa transferred 6.51% (93 µg per beetle) of their total cantharidin content to the hay. After all body parts were removed, 34 ppm of cantharidin was present in a 500-g sample of alfalfa contaminated by crushing 50 beetles onto the hay. Living beetles located below the cut alfalfa transferred less (4.44% or 63 µg per beetle) of their cantharidin to the hay. Recently killed and living beetles transferred significantly greater percentages of cantharidin to hay than beetles that were dead and dried. Male E. occidentalis contained greater amounts of cantharidin (1.28 mg per beetle or 6% body dry weight) than did female beetles (0.87 mg per beetle or 3%body dry weight). Dead beetles, stored for 9 mo at room temperature (25 ± 5°C), contained 34% less cantharidin on a body dry weight basis than did dead beetles kept at -10°C, underscoring the stability of cantharidin and the attendant long-term risk to livestock.