Phyllophaga obsoleta Blanchard is a key pest in Mexican agriculture. Its chemical communication dynamics are partially known. A system of monitoring based on sex pheromones helps reduce the amount of damage it can cause as “white grubs.” To identify the sex pheromone requires many individuals, especially virgin females. Meridic diet and check diet were used to rear larvae. Both substrates were supplied with food for first- and second-instar larvae of P. obsoleta. The effect of each diet on larval survival, weight, and instar transition was evaluated. On Day 175, the meridic diet resulted in more larval weight gain and faster development into third instars than did the check diet. The meridic diet is effective for rearing P. obsoleta in a laboratory.