A Texas AgriLife Extension Service entomologist at Fort Stockton warns alfalfa producers and those buying forage to be on the lookout for blister beetles this simmer.
"Recently, I've been seeing a fairly large outbreak of blister beetles in Reeves County," says Dr. Mark Muegge. "The extent of this outbreak is unknown, but producers need to keep an eye on it. The outbreak could lead to statewide implications since alfalfa from West Texas is shipped all over."
Muegge says serious problems occur when livestock, especially horses, accidentally eat the insects.
"Blister beetles are attracted to blooming alfalfa and a variety of weed hosts, especially silverleaf nightshade and Russian thistle, where they can gather in very large numbers," he says. "Beetles feeding on alfalfa can be crushed into the hay during cutting and baling operations, where animals may later eat them along with the hay."
Muegge emphasizes the problem is not the beetles eating alfalfa, it's the extremely toxic compound called cantharidin they contain. Cantharidin is a blistering agent that when eaten causes severe health issues and risk of death in livestock, especially horses. Dead blister beetles are just as toxic as live ones and remain so for months—even dead. Thus, the blister beetles ruin any hay they are in.
Catharidin poisoning symptoms, called cantharidiasis in horses, are many and varied, according to Muegge, but often include blistering of the mouth, esophagus, stomach and bladder. Colic or diarrhea containing blood and/or muscosal linings may be signs of poisoning.
"Research has shown a lethal does in horses to be 0.5 to 1 milligram of cantharidin per pound of body weight," Muegge says. "Because the toxin varies considerably among the blister beetle species, it's hard to fiutre how many beetles must be eaten to kill a horse. Cantharidin concentrations average from about 0.4 to 5.2 milligram per beetle in some of the blister beetles commonly found in West Texas alfalfa. So a healthy 1,200 pound horse would have to eat about 115 of the most toxic beetles for death to occur."
Beetles vary in size and shape, but nearly all adults have distinctly narrow necks and large heads. The most common species found in West Texas alfalfa are solid velvety gray or rust-colored, or entirely dull black. Adults range from 5/8 to an inch long.
Muegge says outbreaks are worst from early June through August.
"Since dead beetles are still lethal, killing them isn't the answer," he says. "Besides the immature stage of the beetle we're most concerned about loves to eat grasshopper eggs, which most would agree is a good thing, especially this year when most of the state is being overrun with hoppers.
"No, the trick here is to keep the beetles happy, healthy, and alive, so they'll move on out of the alfalfa and take their toxin with them."