part of insect visual primordium formation optic lobe and Bolwig's organ precursor formation optic lobe placode formation GO:0001744 biological_process GO:0007457 Establishment of the optic lobe placode. In Drosophila, for example, the placode appears in the dorsolateral region of the head in late stage 11 embryos and is the precursor to the larval visual system. insect visual primordium development ectodermal placode formation