Fitness Trade-Offs and Potential Metabolic Resistance Mechanisms in Geographically Distinct Strains of Trichogramma dendrolimi: Implications for Imidacloprid Resistance Management

The widespread use of neonicotinoid insecticides has led to increasing resistance in non-target organisms, including the egg parasitoid <i>Trichogramma dendrolimi</i>, a crucial biological control agent. Film-residue bioassays on 17 geographic strains revealed striking inter-strain variability in susceptibility to imidacloprid, with mortality at a discriminating dose of 0.1 mg/L ranging from 25.7% to 87%. The most tolerant (FS) and least tolerant (HA) strains were subsequently selected for evaluation of biological parameters and comparative transcriptomics. Tolerant strains (FS) showed adaptive trade-offs: extended longevity (5.47 ± 0.57 d) and emergence (93.6 ± 1.9%), but reduced fecundity (54.6 ± 4.9 eggs) compared to HA. Transcriptome analysis revealed 2115 differentially expressed genes, with GO enrichment highlighting metabolic and detoxification pathways. KEGG analysis the most enriched pathways were "Protein digestion and absorption" and "Neuroactive ligand-receptor interaction". RT-qPCR confirmed overexpression of <i>CYP4C1</i>, <i>CYP6K1</i>, and <i>GstS1</i> in FS, indicating their potential roles in metabolic resistance if present. This study presents preliminary evidence of potential fitness trade-offs and molecular mechanisms that could underly imidacloprid resistance in <i>T. dendrolimi</i>, which may lead to important insights for resistance monitoring and more sustainable integrated pest management strategies.