Comparative transcriptomic analysis of Metisa plana: downregulation of cry toxin receptors and detoxification genes in populations with reduced susceptibility to Bacillus thuringiensis biopesticide

Metisa plana Walker (Lepidoptera: Psychidae) is a major defoliator in oil palm plantations. The continuous application of Bacillus thuringiensis (Bt) bioinsecticide has raised concerns about its declining efficacy. In this study, we report the first comparative transcriptomic profiling of M. plana populations exhibiting reduced susceptibility to Bt Cry toxin. Bioassays using the leaf-dip method revealed a 5.44-fold increase in LC₅₀ values between populations, indicating early signs of reduced susceptibility. De novo transcriptome assembly generated 114,860 unigenes and 261,955 transcripts. Differential expression analysis identified 4507 significantly regulated unigenes, including those encoding key Cry toxin receptors such as cadherin, aminopeptidase-N, alkaline phosphatase, and ABC transporters. Notably, three cadherin unigenes were downregulated in the reduced-susceptibility group, suggesting altered receptor expression may contribute to Bt response variation. Selected unigenes were validated via qRT-PCR. This study provides novel insights into the molecular response of M. plana to Bt Cry toxin exposure and offers a foundation for future functional validation and resistance management strategies.