FIGURE 6.8 Scarab beetles (Scarabaeidae). (A) Onthophagus polyphemi; (B) Copris minutus. (From Woodruff, 1973.)

content so that forage crops that are harvested for livestock feed continue to be a source of the toxin. Blister beetles in alfalfa (Medicago sativa) fields contain enough cantharidin to provide lethal doses to horses that feed on this materia) when it is used as hay. Species that pose problems in the United States include the striped blister beetle {Epicauta vittata}, the black blister beetle (E. penn-sylvanica) (Fig. 6.2), the margined blister beetle (E. pestífera), and the three-striped blister beetle (E. lemniscata), as well as E. fabricii, E. occidentales, and E. temexa. Individual beetles contain <0.1 to >11 mg of cantharidin, equivalent to <0.1 to >12% of their dry weights, with males of several species averaging >5%. The minimum lethal dose for a horse is about 1 mg/kg, which means that depending on the size of a horse and the cantharidin content of the beetles ingested, anywhere from 25 to 375 beetles are sufficient to cause death (Capinera et al. 1985).

Horses have been poisoned by eating forage in the southern, midwestern, and western United States. Poisoning is not limited to a particular geographic area because contaminated forage is transported over long distances. Affected animals exhibit moderate to severe clinical signs, ranging from depression to shock that may be followed by death. Abdominal distress (colic), anorexia, depression, and oral irritation are commonly observed. These signs are accompanied by markedly decreased serum calcium and magnesium. Accelerated heart rate (tachycardia), increased respiratory rate (tachypnea), and increased creatinine kinase activity are indicative of severe toxicosis that is likely to lead to death. In most cases in which death has occurred, a horse has succumbed within 48 hr of the onset of clinical signs. Horses are the most commonly affected because the kinds of forage they are fed are most often contaminated with beetles. Although the ruminant digestive tract is less susceptible to cantharidin poisoning, goats, sheep, and cattle have also died from cantharidin toxicosis.

Horses and cattle have also been poisoned by pederin following ingestion of the tropical staphylinid P.fuscipes. Pederin can cause severe damage to the mucosa of the alimentary tract.

Historically, there are reports of chickens, ducklings, goslings, and young turkeys dying as a direct result of ingesting the rose chafer (Macrodactylus subspinosus), a member of the Scarabaeidae (Lamson 1922). Although this North American species is abundant in the summer months, modern enclosed poultry production facilities may have gready reduced the incidence of such poisonings.

Darkling beedes (Tenebrionidae) inhabiting farm buildings can be mechanical vectors of animal pathogens. Tenebrionid beetles infesting feed in chicken houses may become infected with Salmonella bacteria passed in feces from infected chickens. Both larval and adult forms of the lesser mealworm beetle (Alphitobius diaperinus) (Fig. 6.9) have been found to maintain viable pathogens (e.g., Salmonella typhimurium and S. chester) on their external surfaces and in their digestive tracts. The bacteria survive for days after infection and are disseminated via beetle excreta. In chicken-breeding facilities, grain beetles are potential disseminators of these pathogens

FIGURE 6.9 Lesser mealworm, Alphitobius dinperinus (Tenebrionidae), larvae and adults in poultry litter. (Photo by G. R. Mullen.)

FIGURE 6.8 Scarab beetles (Scarabaeidae). (A) Onthophagus polyphemi; (B) Copris minutus. (From Woodruff, 1973.)

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