An artificial diet for lepidopteran insects of the present invention, including: a protein; and a carbohydrate, wherein a content of a stable isotope is equal to or greater than 50 atom %. A method for producing an artificial diet for lepidopteran insects, including: a defatting treatment step of subjecting a microorganism to a defatting treatment; a hydrothermal solution extraction treatment step of subjecting the microorganism to an extraction treatment using a hydrothermal solution; and a mixing step of mixing a carbohydrate and a protein originated from the microorganism that is subjected to the defatting treatment step and the hydrothermal solution extraction treatment step.