Chitin metabolism as a potential target for RNAi-based control of the forestry pest Hyblaea puera Cramer (Lepidoptera: Hyblaeidae).

Background: Hyblaea puera, commonly known as the teak defoliator, is a serious pest in teak plantations. Despite the availability of control measures, this pest causes losses in yield and quality of timber through voracious feeding. RNA interference (RNAi) is a promising strategy for the control of this pest. Chitin metabolism, which is vital for the growth and development of arthropods, is a potential target for developing RNAi-based insecticides.

Results: To assess the effects of chitin metabolism inhibition, H. puera larvae were treated with a chitin synthesis inhibitor, diflubenzuron (DFB). DFB treatment caused pupal deformities and disrupted eclosion. Partial gene sequences for three key genes of H. puera chitin metabolism were cloned and sequenced: chitin synthase 1 (HpCHS1), chitinase-h (HpChi-h) and ecdysone receptor (HpEcR). Feeding dsRNA cognate for these three target genes to the first instar of H. puera resulted in mortality and reduction in the corresponding transcript levels as assessed through qRT-PCR. This is the first report of RNAi in this forestry pest. The highest mortality was 45.9%, in response to dsHpEcR treatment; HpChi-h transcripts were the most down-regulated in response to dsHpEcR feeding. DsHpEcR RNAi resulted in growth inhibition and molting arrest. The mortalities were 29.7% and 32.4% for dsHpCHS1 and dsHpChi-h feeding, respectively.

Conclusion: Chitin metabolism could be a potential target for RNAi-based control of H. puera, and HpCHS1, HpChi-h and HpEcR could be suitable target genes. However, the RNAi efficacy needs to be improved through formulations that improve stability and uptake, and employing better delivery strategies. © 2021 Society of Chemical Industry.