This study discovered that special fungi living inside white spruce trees help protect the trees from damaging insects called budworms. These fungi produce toxic substances and smelly compounds that kill or repel the budworms. When researchers increased the amount of these beneficial fungi in young spruce trees, the trees produced higher levels of protective chemicals called terpenes. This research shows that the relationship between spruce trees, fungi, and insects has evolved together over time, with fungi playing a crucial role in keeping trees healthy.