Scientists used UV light to create improved mutant strains of a fungus that naturally kills insect pests. The best mutant strain showed increased ability to survive harsh environmental conditions like heat and oxidative stress, while becoming more effective at infecting target pest insects. This improvement makes the fungus more practical for use as a natural pesticide in fields exposed to sunlight. Gene analysis revealed the mutant fungi enhanced certain protective proteins while reducing reliance on traditional antioxidant systems.