Oklahoma State University Stillwater, OK
Oklahoma Alfalfa Oklahoma Cooperative Extension Service Oklahoma Agricultural Experiment Station

BLISTER BEETLES IN ALFALFA
Although several species occur in the southern plains region, the two species of blister beetles most commonly found in alfalfa grown in the region are the striped blister beetle and black blister beetle. These beetles complete one generation per year that begins in late summer when adults lay eggs in cracks or cavities in soil. Upon hatching, larvae of blister beetles locate grasshopper egg masses in soil and consume them. After consuming the grasshopper eggs, blister beetle larvae enter the pupal stage to overwinter in soil.    Adult blister beetles emerge in May and June and feed on a wide variety of plants, one of which is alfalfa. Blister beetles are so named because they contain a blistering agent called "cantharidin", which is quite irritating to skin and other tissues of animals. It is the presence of cantharidin in their bodies that causes blister beetles to be pests in alfalfa. Striped blister beetles, in particular, often gather in large numbers called swarms in alfalfa fields. When large numbers of these beetles within swarms are killed at alfalfa harvest, as may occur if hay is crimped when cut or machinery is driven over windrows, highly toxic doses of cantharidin in bodies of dead beetles can be baled into hay.    Cantharidin can cause severe toxic reactions by damaging the stomach lining, kidneys, and urinary tract of animals that are fed infested hay. Horses are particularly susceptible to this type of injury, and the bodies of as few as 15-20 beetles consumed in hay may be sufficient to cause a severe, toxic reaction. It is critical that precautions be taken to reduce chances of contamination of hay whenever it is to be fed to horses. See OSU Extension Facts #2072 for additional information on avoiding contamination of hay by blister beetles.
Richard Berberet, Alfalfa Entomologist  Department of Entomology and Plant Pathology  Oklahoma State University

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