Cantharidin production in a blister beetle

Abstract

Cantharidin, a potent defensive chemical, is present in all ten life stages of the blister beetle Epicauta funebris. The first five larval stages accumulate cantharidin as they feed and grow in size. When disturbed, they exude cantharidin in a milky oral fluid, not in hemolymph which adult beetles reflexively discharge from leg joints. Two subsequent larval stages and the pupa do not feed, grow, regurgitate, or change in their defensive reserves (110 micrograms cantharidin/insect, regardless of sex). Adult beetles kept in isolation for 60-90 d exhibit a pronounced sexual dimorphism in cantharidin production: the male biosynthesizes about 17 mg of the toxin, representing 10% of his live weight, whereas the female actually loses most of her defensive reserves. But in the wild a female beetle repeatedly acquires cantharidin as copulatory gifts from her mates.

Cantharidin Revisited

“…4 The male beetle synthesizes cantharidin for use as a defense mechanism, and the female acquires cantharidin as a copulatory gift from her mate. 5 Blister beetle dermatosis is a seasonal vesiculobullous skin disorder that occurs several hours after contact with the beetle. 4 If contact with a beetle is noted, blowing off the beetle, rather than brushing it off, will minimize cantharidin exposure.…”

Cantharidin is conserved across phylogeographic lineages and present in both morphs of Iberian Berberomeloe blister beetles (Coleoptera, Meloidae)

“…A second function of cantharidin could also be to help blister beetles avoid internal parasites, due to its fungicidal, nematocidal, and bactericidal properties (Carrel & Eisner, 1974;Bravo et al, 2014). Among blister beetles, males usually have more cantharidin than females (Capinera, Gardner & Stermitz, 1985;Blodgett, Carrel & Higgins, 1991;Carrel et al, 1993;Carrel, 1999;Nikbakhtzadeh & Tirgari, 2002;Mebs et al, 2009;Nikbakhtzadeh et al, 2012), and apparently only males are able to synthesize this toxin (Sierra, Woggon & Schmid, 1976;Holz et al, 1994). Therefore, cantharidin content could also be under sexual selection pressures.…”

Chemical Protection of Insect Eggs

“…In the meloids, males are mostly the ones who biosynthesize cantharidin from a methyl farnesoate intermediate (McCormick and Carrel, 1987), even though cantharidin synthesis was observed in both sexes of Epicnutu and Meloe larvae (Meyer et al, 1968;Carrel et al, 1993). Males of the genera Lyttu and Epicnuta are within the Eggs known to transfer cantharidin to the female with their sperm during mating (Sierra et al, 1976;Carrelet al, 1993;Dettner, 1997).…”