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

## TL;DR

This study explores how different strains of a wasp species resist a common insecticide, revealing biological trade-offs and potential genetic markers for resistance.

## Contribution

The study identifies specific genes linked to insecticide resistance and highlights fitness trade-offs in resistant wasp strains.

## Key findings

- The FS strain shows greater survival but reduced reproduction when exposed to imidacloprid.
- Genes CYP4C1, CYP6K1, and GstS1 are overexpressed in the FS strain and may contribute to resistance.
- Transcriptomic analysis reveals metabolic and detoxification pathways as key to resistance mechanisms.

## Abstract

This study helps understand the phenotypic and molecular basis of imidacloprid resistance in Trichogramma dendrolimi. The tolerant FS strain has distinct biological trade-offs including less fecundity but greater survival when exposed to insecticide. According to transcriptomic and RT-qPCR analyses, CYP4C1, CYP6K1, and GstS1 were found to play a role in detoxification and can be potential targets for resistance monitoring and management. The findings will help in enhancing the understanding of resistance evolution and strategies for sustainable pest control.

The widespread use of neonicotinoid insecticides has led to increasing resistance in non-target organisms, including the egg parasitoid Trichogramma dendrolimi, 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 CYP4C1, CYP6K1, and GstS1 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 T. dendrolimi, which may lead to important insights for resistance monitoring and more sustainable integrated pest management strategies.