Unraveling the role of male gonads and haemolymph in cantharidin-exuding Lydus trimaculatus and Mylabris variabilis (Coleoptera: Meloidae): a comparative transcriptomics approach

Meloidae (blister beetles) are known to autogenously synthetize cantharidin (CA), a toxic and defensive terpene chiefly stored in male gonads and emitted outward through reflex-bleeding. Despite recent advancements on the molecular basis of CA biosynthesis in Meloidae, both the biochemical pathway (likely related to Mevalonate and Juvenile Hormone) and definition of the production organ(s) are still uncertain. Moreover, some relevant aspects on how self-protection from the accumulation and transport of CA is achieved in blister beetles and regulation of their auto-haemorrhaging responses have been experimentally neglected. To provide hints on these pending questions, we performed a comparative de novo assembly transcriptomic analysis of two Meloinae members, Lydus trimaculatus (tribe Lyttini) and Mylabris variabilis (tribe Mylabrini) and characterised the differential expression profile of male gonads and reflex-bled haemolymph.