Starvation of immature boll weevils resulting from square desiccation is considered a major determinant of natural mortality. However, the critical weight below which a larva cannot complete development without further feeding has not been determined. Critical weights of second and third instars were investigated using food-removal techniques, and the age and size distributions of larvae in newly abscised squares were estimated from field collections. Second instars examined averaged 3.22 mg in weight and ranged from 0.23 to 5.55 mg. About 80% of second instars weighing ≥1.67 mg molted, but none pupated. The estimated critical weight for 50% of unfed second instars to survive to third instar was 2.49 mg. Third instars examined averaged 14.64 mg in weight and ranged from 1.81 to 34.43 mg. About 64% of third instars weighing ≥5.29 mg developed into adults, ranging in weight from 1.61 to 21.49 mg and averaging 10.44 mg. Estimated critical weights for 50% of unfed third instars to survive to the pupal and adult stages were 6.63 and 8.89 mg, respectively. The estimated critical weight for 50% of pupae to survive to adulthood was 4.52 mg. Larvae collected from newly abscised squares were predominantly second (56%) and third instars (39%). Furthermore, an estimated 19% of all larvae collected were capable of development to adulthood without further feeding. In light of the rapid rate of larval growth and development, our results suggest that square desiccation sufficient to deter feeding by larvae must occur within 1–3 d of square abscission to produce a high proportion of starvation-induced mortality.