Cantharidin content in two Mediterranean species of blister beetles, Lydus trimaculatus and Mylabris variabilis (Coleoptera: Meloidae)

Abstract

Cantharidin (CA), a toxic terpene produced by blister beetles (Coleoptera: Meloidae), attracts the interest of many researchers for its renowned medical properties. The CA content in blister beetles has been mainly quantified in some Oriental species, due to their use in traditional Chinese medicine, or in few other species of toxicological importance. As CA quantification has been largely ignored in many other members of this family, we aimed at estimating CA content in natural populations of two of the most abundant species in central Italy, Mylabris variabilis and Lydus trimaculatus. Nearly 100 individuals for each species were collected in the field, identified and reared in fauna‐boxes until CA collection. Available protocols were optimized for CA extraction from both dried‐body tissues and exuded hemolymph collected from leg joints using capillary tubes. The CA content was quantified in a gas chromatography system coupled to a mass spectrometer using a calibration curve with diethyl‐ester of norcantharidin as the internal standard. We observed: (i) high variability in CA content among specimens, which was positively related to individual dry‐weight; and (ii) slightly larger (though non‐significant) amount of CA in males than in females for both species. Our data are consistent with the available published reports about CA content, transfer and distribution in blister beetles and suggest a conserved biological role of this terpene in Meloidae.

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

“…Males of Meloidae are known to contain higher concentrations of cantharidin than females [ 39 , 44 , 45 ]. Our results showed no sex-specific differences in cantharidin concentration, which was also reported regionally by Gisondi et al [ 8 ]. The absence of a significant difference between males and females can be attributed to the transfer of cantharidin from males to females during copulation [ 8 , 27 , 46 , 47 ].…”

“…In various studies, concentrations of less than 0.04 to up to 30.3 mg of cantharidin per individual beetles have been found [ 2 , 38 ]. Gisondi et al [ 8 ] examined the cantharidin concentration of M. variabilis collected in central Italy and reported the range between 0.001 and 0.994 mg per beetle, with the highest concentrations being significantly higher than cantharidin content found in this study. Nikbakhtzadeh and Tirgari [ 39 ] reported similar results for the same species collected in Hamedan province, Iran.…”

“…The absence of a significant difference between males and females can be attributed to the transfer of cantharidin from males to females during copulation [ 8 , 27 , 46 , 47 ]. The cantharidin concentrations in this and other studies should, therefore, be attributed to a well-known phenomenon of variation in titers of arthropod chemical defense depending on their biology, sex, age, size, and reproductive status [ 8 , 40 , 44 , 48 ].…”

“…The concentration of cantharidin in Meloid beetles in the northern Mediterranean area has already been studied and appears to be similar to that in regions where the disease is more endemic [ 8 ]. However, Meloid beetles have never been studied as a potential forage contaminant in the region.…”

“…The main function of cantharidin is to protect the eggs of the insects from potential predators [ 4 , 5 , 6 ]. The production of cantharidin varies greatly depending on species, size of the beetle, sex, season, and food source [ 7 , 8 ].…”