We have examined factors affecting neuronal proliferation and cell death during development of the adult outer optic ganglia in the moth Manduca sexta. The role of retinal afferents was addressed by optic nerve section on the first day of pupation, when the retina is only partially formed. Deafferentation by optic nerve section resulted in increased levels of cell death in the medulla cortex but did not affect medulla precursor proliferation. Conversely, division of lamina ganglion mother cells ceased following deafferentation, whereas cell death in the lamina cortex did not increase significantly. Implantation of isolated outer optic anlage into host animals demonstrated that medulla precursor proliferation was independent of centripetal inputs and retinal afferents. The role of developmental hormones in regulating outer optic ganglia development was also investigated. Many events in medulla and lamina development are correlated with changes in the titers of the ecdysteroids, and these events could be prevented by application of a juvenile hormone mimic (JHM). Application of JHM early in the fifth (final) larval instar terminated medulla precursor proliferation and prevented the initiation of lamina precursor proliferation, but application late in the fifth instar (after the commitment peak of ecdysteroids) had little effect on proliferation. Application of JHM on the third or fourth day of pupal life prolonged precursor proliferation and delayed degeneration of the outer optic anlage. Precocious application of 20-hydroxyecdysone on the first day of pupal life accelerated outer optic anlage degeneration but did not cause premature termination of proliferation.