Potential of RNAi Targeting Juvenile Hormone Acid Methyltransferase (JHAMT) for Controlling Dendroctonus valens LeConte (Coleoptera: Scolytidae)

Dendroctonus valens LeConte represents a major invasive pest species in China. Both larvae and adults primarily feed on the phloem of the tree trunk base and roots, disrupting nutrient transport and leading to host tree mortality, which poses a severe threat to forest ecosystems and the forestry economy. Juvenile hormone acid methyltransferase (JHAMT) is a key enzyme in insect juvenile hormone (JH) biosynthesis. In this study, we identified a JHAMT-encoding gene, DvJHAMT, in D. valens via bioinformatic analysis. RT-qPCR analysis revealed that DvJHAMT is predominantly expressed during the egg and larval stages. In the fourth-instar larvae, the highest expression levels were observed in the head and epidermis, suggesting a central regulatory role during this critical developmental period. To investigate its function via RNA interference (RNAi), a nanomaterial, star polycation (SPc), was employed for the transdermal delivery of dsRNA into the fourth-instar larvae. The results demonstrated that DvJHAMT knockdown significantly downregulated mRNA levels, resulting in marked decreases in larval survival, pupation, and eclosion rates. Notably, treatment with 0.7 µg dsDvJHAMT-SPc resulted in a 96.67% mortality rate and a reduced pupation rate of 41.67% at 34 days post-treatment. Furthermore, RNAi led to developmental deformities and significant weight loss in larvae. ELISA assays confirmed that DvJHAMT silencing led to reduced JHAMT enzyme activity and JH III titers in a dose-dependent manner. In conclusion, our findings demonstrate that DvJHAMT plays a vital role in JH biosynthesis and that its suppression exhibits potent lethal effects, suggesting that DvJHAMT is a promising candidate for RNAi-based management of D. valens.