# Bt Exposure-Induced Death of Dioryctria abietella (Lepidoptera: Pyralidae) Involvement in Alterations of Gene Expression and Enzyme Activity

## TL;DR

This study explores how Bacillus thuringiensis (Bt) kills Dioryctria abietella larvae by altering gene expression and enzyme activity, offering insights for better pest control.

## Contribution

The study reveals how Bt exposure affects gene expression and enzyme activity in D. abietella larvae, providing new insights into biocontrol strategies.

## Key findings

- Bt exposure significantly decreased the survival of D. abietella larvae.
- Transcriptome analysis showed altered gene expression patterns in response to Bt exposure.
- Bt05041 strain was the most toxic to D. abietella larvae with an LC50 of 3.15 × 10⁸ CFUs mL⁻¹.

## Abstract

This study investigates the lethal effects of Bacillus thuringiensis (Bt) infection on Dioryctria abietella (Lepidoptera: Pyralidae) larvae. D. abietella is a destructive wood-boring pest that causes significant economic losses to Korean pine forests worldwide. Here, we tested larval survival, enzyme activity, and gene expression to explore the possible mechanism underlying Bt-mediated death in D. abietella larvae. Our findings demonstrate that Bt exposure significantly decreased the survival of D. abietella larvae and altered the activities of antioxidant and detoxification enzymes. Among them, Bacillus thuringiensis galleriae 05041 strain (Bt05041) was the most toxic insecticide. Transcriptome analysis revealed that gene expression in D. abietella changed over time with Bt05041 exposure, and high expression of toxin-receptors enhanced Bt’s insecticidal effect. These findings offer new insights for improving the biocontrol strategies of D. abietella.

Dioryctria abietella (Lepidoptera: Pyralidae) is a destructive forest pest for coniferous trees. Bacillus thuringiensis has been widely applied in forestry as a biological control agent to control it. However, the mechanisms of Bt-induced mortality in D. abietella, particularly its effects on gene expression and enzyme activities, remain unclear. Here, bioassay, enzyme assay, transcriptome sequencing, and gene expression profiling were employed to explore the relationship between the toxin-receptor, defense, and lethal mechanisms of D. abietella after Bt exposure. In a toxicity bioassay, Bacillus thuringiensis galleriae 05041 strain (Bt05041) was the most toxic insecticide to the larvae of D. abietella, with LC50 values of 3.15 × 108 Colony-Forming Units (CFUs) mL−1 at 72 h after treatment. Transcriptome analysis revealed that the gene expression patterns of D. abietella after 8 h of Bt05041 exposure (Bt8) varied considerably from the Bt05041-treated for 2 h group (Bt2). In the Bt2 group, differentially expressed genes were significantly enriched in cellular and bioenergy pathways of lysosome, insulin signaling, cGMP-PKG signaling, etc. Immune-related pathways were activated, namely cAMP, AMPK, MAPK, Rap1, IMD, and Toll pathways. Meanwhile, Bt8 treatment caused metabolic changes in basic substances such as amino acids, glucose, nucleic acids, and fatty acids. Bt05041 exposure activated the activities of defense enzymes and induced gene expression changes in D. abietella larvae. Among them, most Bt-receptor genes had higher expression levels than defense enzyme genes. Overall, these findings reveal a possible mechanism underlying Bt-mediated death in D. abietella larvae. This work provides valuable information in terms of biological control strategies.