Fig. 4

Retinal development in the worker pupae. Histological labeling of frontal sections at approximately the center of the eye with phalloidin (green) and Hoechst 34580 (blue) to label f-actin and nuclei, respectively, were performed to visualize the retinal development of the honey bee compound eyes. a-c: At the beginning of the pupal phase the retina consists only of a thin hypodermis comprising crystalline cone cells, several pigment cells, hair cells (double arrow head in a) and photoreceptor cells which contain the fused rhabdoms (distal and proximal boundaries of the rhabdom are marked by arrow heads) and extend their axons as twisted bundles (double arrow head in c) through the basement membrane. At this early pupal phase rhabdoms are short and all nuclei (except those from the crystalline cone cells) are clustered in the same level. d-h: During the next days of pupal development rhabdoms and photoreceptor cells significantly increase in size, and nuclei of photoreceptor and pigment cells separate from each other into distinct layers (double arrow head in d). The cell nuclei of the ninth photoreceptor cell become first visible in pupal stage P5 and form a distinct layer in P6 (double arrow head in e). i: The retina reached its final stage in freshly eclosed bees (A, adult). Scale bar in all figures: 50 μm