Blister beetle populations could escalate this summer, warns Randy Higgins, Kansas State University extension entomologist.
Because the larvae of some common blister beetle species feed on grasshopper eggs, beetle infestations tend to correlate with grasshopper numbers. And hopper numbers were high in Kansas in 1997, says Higgins. Infestations were reported in several other states as well.
"It makes you wonder about what's going to happen this year," he says.
Blister beetle, or cantharidin, poisoning remains a major concern for hay growers and livestock owners nationwide. While the greatest incidence of death and illness has been in horses, cattle and sheep have been poisoned, too. Laboratory studies have also shown that cantharidin can reduce hay digestibility.
While blister beetles can be found virtually anywhere alfalfa is grown, the risk is greatest west of the Mississippi River.
Common species include three-striped, margined, gray, spotted and black blister beetles. Three-striped blister beetles are the biggest threat.
Striped blister beetles emerge as adults in late June and July, but other species emerge earlier and later, so beetles are a threat throughout the growing season.
Spraying blister beetles with an insecticide doesn't solve the problem, because dead beetles could contaminate the hay.
"Keeping the beetles alive and healthy means that they can remove themselves from the field, thereby minimizing contamination of the hay," says Higgins.
That means cutting alfalfa with a machine that doesn't condition it, such as a self-propelled windrower with the conditioning rolls removed. Most beetles will then leave the field before hay is baled.
Higgins also recommends that growers avoid driving on hay in turning areas to prevent wheel-traffic mortality.
To avoid blister beetles, carefully monitor suspect fields with sweep nets just before harvest. Check with local extension personnel for help in identifying local species, life cycles and emergence periods.
Higgins and his colleagues have brainstormed over the years about potential control methods. Their ideas include:
* Development of an "artificial nose" odor device that detects cantharidin.
* Development of a synthetic pheromone attractant that would lure blister beetle swarms away from alfalfa fields to areas where they could be trapped and killed. Higgins surmises that blister beetles emit a natural pheromone that attracts the pests to one another.
"How else do 60,000 beetles find each other and operate as a group?" he asks.
"It also might be possible to develop a product that disperses swarms, thereby lessening the risk of lethal doses forming if the beetles are killed."
* The use of trained dogs to detect cantharidin in baled hay.
"Just as dogs have been trained by law enforcement agencies to detect low levels of illegal drugs, perhaps they could be taught to zero in on cantharidin," Higgins says.
"Maybe someone could start a business with dogs trained to detect the absence or presence of cantharidin. If the dogs couldn't detect the substance, it's possible the hay could be certified blister-beetle free."
The researchers also theorize that dehydration might break down the cantharidin in hay known to be contaminated, rendering it non-toxic. But so far they haven't been able to test the theory.
"During peak times of operation, nobody wants to give us access to a dehydration plant when we have beetles available.
"Plus, plant operators are worried about us contaminating the equipment. We can't guarantee that there won't be any toxic residues remaining after we're finished," says Higgins.
For more information, access his department's Web site: www.oznet.KSU.edu/entomology