Differential regulation of reproduction and molting by juvenile hormone in aphids

Insects rely on juvenile hormones to regulate various physiological processes, including reproduction and molting; currently eight forms of this hormone are known. In most insects, only JH Ⅲ is synthesized. Meanwhile, aphids produce JH Ⅲ and JH Ⅲ skipped bisepoxide (JHSB₃). However, it remains unclear whether these compounds play distinct roles in functional regulation. In this study, we demonstrated that the tested concentrations of JH Ⅲ effectively increased the number of aphid offspring, whereas high concentrations of JHSB₃ affected the molting process. Drip experiments showed that 10 mg/L JH Ⅲ increased the number of offspring from 39.38 ± 8.03 to 56.50 ± 13.17, whereas 10 mg/L JHSB₃ resulted in a 60.00 %± 5.77 % failure rate in molting before adulthood. Transcriptomic analysis also revealed that in the JH Ⅲ treatment group, 9 genes and 7 pathways associated with reproduction were expressed, but not genes or pathways associated with molting. In addition, 16 genes and 9 pathways associated with molting as well as 5 genes and 4 pathways associated with reproduction were identified in the JHSB₃ treatment group. JH Ⅲ promotes reproduction in aphids by enhancing Vg expression, whereas JHSB₃ affects molting by inhibiting the synthesis of molting hormone-related enzymes. The results indicate that JH Ⅲ and JHSB₃ exhibit diverse functions in Aphis craccivora. The findings have significant implications for further studies on the physiological functions of different JHs.