Entomological Surveillance and Cantharidin Concentrations in Mylabris variabilis and Epicauta rufidorsum Blister Beetles in Slovenia

SIMPLE SUMMARY: True blister beetles (genus Epicauta, family Meloidae) produce cantharidin, which is a potent blistering agent. Cantharidin toxicosis is well documented in humans and animals. Drought and modern harvesting techniques are thought to increase the likelihood of blister beetle contamination of forage and cantharidin intoxication in animals. Local presence, behavioral patterns, and cantharidin concentration were studied in Mylabris variabilis and Epicauta rufidorsum. In this study, E. rufidorsum was found to be the most likely source of forage contamination due to its local abundance, swarming activity, and tendency to reside in the green parts of plants after cutting. Cantharidin was detected in the bodies of both blister beetles species studied. It is likely that modern forage harvesting methods, which involve simultaneous processing of forage after cutting, increase the incidence of cantharidin toxicoses in animals. Delaying these processes by a few minutes would reduce the likelihood of Epicauta contamination of the forage. ABSTRACT: True blister beetles (genus Epicauta, family Meloidae) produce cantharidin, which can cause toxicosis in humans and animals. Some recent reports suggest that poisoning by the blister beetle has occurred in the Mediterranean part of Slovenia, which has never been reported before. Drought and modern harvesting techniques are thought to increase the likelihood of blister beetle forage contamination and cantharidin intoxication in animals. A survey of fields associated with blister beetle contamination was conducted and the Meloid species present were identified. Entomological surveillance was conducted for Mylabris variabilis and Epicauta rufidorsum. Cantharidin concentrations were also measured in both blister beetle species. Cantharidin concentration in Mylabris variabilis (n = 17) ranged from 0.038 to 0.354 µg/mg (mean 0.151 µg/mg). Cantharidin concentration in Epicauta rufidorsum (n = 36) ranged from 0.055 to 0.341 µg/mg (mean 0.142 µg/mg). Both species exhibited variable concentrations of cantharidin that could not be associated with their biology, sex, age, size, and/or reproductive status. Epicauta rufidorsum have never previously been studied as a possible source of forage contamination, nor have cantharidin concentrations been determined in this species. It is the most likely source of forage contamination due to its abundance in the investigated fields, its swarming activity, and its tendency to reside in the green parts of plants immediately after cutting. Delaying the simultaneous processing and storage of forage after cutting would reduce the likelihood of forage contamination by blister beetles, as they can then retreat to the ground or fly away.