Nutrition during juvenile development is a key determinant of insect fitness, shaping growth and survival. The alfalfa leafcutter bee (Megachile rotundata) is one of the most important managed insect pollinators. Juvenile (larval) nutrition plays a crucial role, since the quality and quantity of food provided through one-time provisioning by the mother bee determines later life-stage fitness and survival. To examine how specific macronutrients shape these outcomes, larval diets were manipulated through a geometric framework spanning protein-to-carbohydrate ratios from 1:2.2 (protein-rich) to 1:5.1 (carbohydrate-rich) with a total of nine diet treatments. Larvae reared on these diets were tracked through development stages, and prepupal weights were recorded. Protein-to-carbohydrate balance significantly affected prepupal weights across diet treatments (p<0.05). Diet composition also shaped the pace at which larvae progressed through specific development stages (p<0.05). Bees reared on the richest diet in both protein and carbohydrate content spent more time actively feeding in the fifth instar stage and less time spinning cocoons, whereas the most nutrient-limited diet showed the opposite pattern. Kaplan-Meier survival analysis showed no significant difference in prepupal survival across the nine diet treatments. This indicates that macronutrient composition does shape larval growth trajectory without impacting overall survival. However, the prepupal weights are closely tied to overwintering survival success in this species. The prepupae are currently overwintering, and their post-diapause survival and emergence will be assessed once diapause is complete. This study will be helpful in strengthening the resilience of the managed M. rotundata populations that alfalfa growers depend on for pollination.