Scientists discovered that a virus living inside a beneficial fungus is responsible for the fungus’s ability to kill insect pests. When they removed the virus, the fungus completely lost its ability to penetrate and infect insects through their skin, but could still cause infection if injected directly into the insect’s body. This finding suggests that the virus controls a key enzyme needed for the fungus to break through the insect’s protective outer layer, opening new possibilities for creating more effective biological pest control agents.