Blister beetles have emerged in North Dakota, posing a potential danger to livestock, particularly horses. These beetles produce a toxin called cantharidin, which can cause blistering of the skin when released.
The beetles are attracted to blooming alfalfa fields and weeds such as goldenrods and dandelions. Feeding on nectar, pollen, leaves, stems, and flowers, they can severely harm alfalfa crops.
Horses may experience severe consequences from cantharidin ingestion, including depression, inflammation, mouth ulceration, gastrointestinal tract irritation, and painful urination. Cattle and sheep are more tolerant. Blister beetle species like ash-gray, black, striped, and Nuttall's blister beetles are easily identified due to their narrow neck region.
Blister beetles are very nomadic and tend to congregate in big numbers in specific fields. Once they begin to blossom, they can spread from field borders with host plants like sweet clover into lucerne fields. They may migrate to other flowering field crops once lucerne is cut. Hay infested with blister beetles is a major hazard for hay producers and livestock owners.
To minimize the risk of blister beetles:
1. To avoid crushing the beetles and releasing poisons into the hay, use disc mowers without hay conditioners or crimpers. This makes the beetles want to flee the field.
2. Allow cut hay to dry completely before raking to allow insects to leave. Although raking may clear dead insects, cantharidin may still be present.
3. Control weed hosts that are blossoming near or within lucerne fields.
4. Alfalfa should be harvested when it is less than 10% blossomed or when it is late in the season (mid-August to early September).
5. Inspect fields 24 hours before cutting to ensure there are no new swarms.
6. Avoid using hay suspected of blister beetle contamination for horses. If symptoms like blood-tinged urine or depression appear in horses fed alfalfa, seek veterinary assistance immediately.
7. Cattle can consume hay with blister beetles, but caution is advised. Offer alternative clean hay sources or blend hays. Grinding the hay and mixing it with other feeds dilutes the toxin but does not eliminate it.
8. Chemical control during harvest is generally not recommended, as dead beetles could still be present in cured hay.
If blister beetle toxicity is suspected, diagnostic tests are available through the NDSU veterinary diagnostic laboratory. Plasma or urine samples can be used for testing. For more information regarding test visit https://www.vdl.ndsu.edu/tests/blister-beetle-toxin-cantharidin/ Additional guidance on blister beetle identification and management is accessible through NDSU Extension resources, and local Extension agents can assist with identification and recommend appropriate management strategies.
Photo Credit: GettyImages-Patrick Jennings
Categories: North Dakota, Livestock