A Farnesyl Pyrophosphate Synthase Gene Is Expressed in Fat Body Regulates Cantharidin Synthesis in Male Epicauta impressicornis Blister Beetle

Blister beetles of Epicauta impressicornis have attracted attention because they contain a large amount of cantharidin (CTD). To date, however, the synthesis and transfer of CTD in adults of E. impressicornis are largely unknown. Here, we showed that the larvae E. impressicornis are capable of synthesizing CTD and they consume CTD during pupation. Before sexual maturity, both male and female adults synthesized a small amount of CTD, while after sexual maturity, males produced larger amounts of CTD, but females did not. The newly synthesized CTD in males first appeared in the hemolymph and then accumulated in the reproductive system. During the mating, the males transferred CTD to the reproductive system of females. In addition, a farnesyl pyrophosphate synthase (FPPS) gene was identified in male E. impressicornis. RNA-seq analysis, quantitative RT-PCR, and RNA interference analyses were conducted to investigate expression patterns and the functional roles of E. impressicornis FPPS (EiFPPS). Our results indicate that EiFPPS is highly expressed in the fat body of males. Moreover, the knock-down of EiFPPS led to a significant decrease in CTD synthesis. The current study indicates that EiFPPS is expressed in the fat body to regulate CTD synthesis in male E. impressicornis blister beetles.