Which alfalfa pest is known to produce a toxin that can be toxic to horses?

• A. Garden webworm
• B. Alfalfa weevil
• C. Blister beetle
• D. Cowpea aphid

Answer: (C)

The main concept here is that a specific alfalfa pest can introduce a toxin into hay that is dangerous to horses. Blister beetles contain cantharidin, a potent blistering compound. If alfalfa hay is cut or baled with these beetles, the toxin can remain active in the dried hay and be ingested by horses, potentially causing severe illness or death. Horses may show signs such as mouth irritation, drooling, abdominal pain or colic, increased urination, and in serious cases kidney damage. This risk makes blister beetles unique among common alfalfa pests in terms of toxicity to horses.

The other pests listed do not produce toxins that harm horses simply through feeding on alfalfa. Garden webworm, alfalfa weevil, and cowpea aphid mainly cause physical damage to the plant or reduce forage quality and yield; they don’t introduce a toxic compound into the hay that would poison horses.