Blister Beetle Activity Continues - Sept. 5, 2024

In a July Pest e-Alert, early season blister beetle activity was reported in alfalfa, pasture, and lawns (EPP 23-14). As stated in the report, the striped blister is generally the beetle of most concern for Oklahoma alfalfa producers (Fig. 1). This species makes up 75% of all blister beetles present in Oklahoma and has the highest levels (5mg/beetle) of Cantharidin, the blistering agent that can cause sickness when ingested by livestock, especially horses. Also keep in mind, cantharidin is a very stable compound that can withstand degradation with heating and drying. Thus, if the beetles are present in an alfalfa field and are crushed in the harvesting process, the toxin will still be present in the baled hay.

 

Figure 1. Striped blister beetle. Photo: Oklahoma State University.

 

While populations begin to build early in the season, July – August are peak months where we find blister beetle activity in Oklahoma. This activity can continue into early September; therefore, potential for hay contamination from this pest remains. In addition to the more common striped blister beetle (Epicauta occidentalis), throughout the summer, we have also observed the black blister beetle (Epicauta pensylvanica), and ash gray blister beetle (Epicauta fabricii) in field monitoring, Epicauta conferta (Fig. 2) in pastures, and have received numerous reports of the black blister beetle on home ornamentals and vegetables. As recently as last week (8/26/2024), E. occidentalis, E. pennsylvanicus, and E. fabricii, were identified in an alfalfa producer’s field west of Stillwater (Logan County).

 

As in Oklahoma, other states appear to be seeing an uptick in blister beetle activity this year. Striped blister beetles are commonly found throughout the southern and eastern states during the summer months (Fig 3). Weather patterns consistently exhibiting hot, dry conditions with intermittent rainfall can increase blister beetle populations. In addition, due to their predation on grasshopper eggs as larvae, blister beetles are more likely to be present in areas where large grasshopper populations were observed during the previous year. 

 

Figure 2. Epicauta conferta on Sericea Lespedeza in Payne County. Photo by J.A. Cammack.

 

Figure 3. Distribution of reported striped blister beetle throughout the United States. Photo: Oklahoma State University.

 

As previously stated, several other species may also be present in alfalfa, including (E. fabricii) or ash gray blister beetle. While cantharidin levels are significantly lower in other species (0.5 mg/beetle), compared to striped blister beetles, poisoning to animals that are fed infested hay can still occur (Fig 4).

 

Figure 4. Black margined, spotted, ash gray, black, and stiped blister beetles. Photo: Oklahoma State University.

 

This is the time of year when hay supplies may be dwindling, or livestock owners are stocking up for winter feeding. At times, this may mean searching for out of state hay resources. We have recently gotten a report of an Oklahoma horse owner buying out of state hay that was infested with ash gray blister beetles. While horses are most affected by cantharidin poisoning, cattle and sheep are also susceptible. 

 

Levels of cantharidin can vary. The accidental or inadvertent ingestion of as few as 23 beetles (Table 1.) can be fatal for horses depending on the species, age, and overall health, highlighting the importance of vigilant management and prevention practices. 

 

 

If blister beetles are found or even suspected, do NOT feed the alfalfa to horses or any other livestock. Simply removing the beetles will not eliminate the toxic contamination by cantharidin.

 

Therefore, awareness and proactive management among hay producers and livestock owners is crucial for management of this pest.

 

For alfalfa producers:

Blister beetle contaminated hay is almost always the result of beetles being crushed prior to baling. 

 

• Don’t use crimpers when cutting hay.
• Remains of blister beetles may be concentrated in a small portion of the hay from a field.
• Avoid wheel traffic.
• Maintain weed control within and outside the field.
• Spraying fence rows and field borders can help prevent migration into fields.
• Harvest before bloom, if possible.
• Match cuttings and markets. Early-May and late-September harvests are before and after the major blister beetle season. Target these cuttings for horse buyers.  

 

Things a buyer should do:

• Know your alfalfa supplier.
• Ask producers what precautions were taken to avoid the presence of blister beetles in forage.
• Inspect hay before feeding if presence of blister beetles is suspected.
• If feeding small amounts of alfalfa, examine each flake for concentrations of dead blister beetles.
• Purchase hay harvested before May or after September. This will not guarantee a lack of problems with blister beetles but will reduce the risks significantly.
• Clinical signs can begin to appear 3-6 hours after ingestion. Aggressive therapy, if caught early, can help with survival rates
• If symptoms appear, call your veterinarian immediately.

 

For more information on blister beetles in Oklahoma, go to EPP-2072, Blister Beetles in Alfalfa.