Effect of Selection for Low and High Varroa destructor Population Growth Rates on the Honey Bee Transcriptome

Area of Science:

• Entomology
• Animal Genetics
• Immunology

Background:

• Varroa destructor poses a significant threat to honey bee (Apis mellifera) populations worldwide.
• Selective breeding for Varroa resistance offers a sustainable, long-term solution to parasitism.

Purpose of the Study:

• To investigate the genetic and molecular differences between honey bee genotypes selected for low (resistant) and high (susceptible) Varroa destructor population growth.
• To understand the molecular mechanisms underlying Varroa resistance in honey bees.

Main Methods:

• Three generations of selective breeding were performed to establish low Varroa growth (LVG) and high Varroa growth (HVG) honey bee lines.
• Transcriptome analysis (RNA sequencing) was used to compare gene expression profiles between LVG and HVG bees upon Varroa parasitism.

Main Results:

• LVG bees demonstrated enhanced behavioral, cellular, and humoral immunity against Varroa compared to HVG bees.
• Parasitized LVG bees displayed fewer differentially expressed genes (DEGs) than HVG bees, suggesting a reduced impact of Varroa.
• Gene expression analysis revealed genotype-specific alterations, with LVG bees showing up-regulation of odorant binding proteins and down-regulation of the corazonin receptor, potentially related to resistance.
• HVG bees showed up-regulation of ATP synthase and down-regulation of the transcription factor dorsal, possibly indicating a stress response.

Conclusions:

• Selection for low and high Varroa destructor population growth resulted in distinct honey bee genotypes with significant differences in gene expression during parasitism.
• These gene expression differences are likely associated with the observed resistance and susceptibility to Varroa, offering insights into breeding strategies for mite-resistant honey bees.