In the embryo, there is a strong maternal contribution which masks the zygotic expression until about stage 15, when a weak signal can be detected in the embryonic midgut. Since their cuticle is transparent, third instar larvae are easy to score under the fluorescent dissecting microscope. The main GFP expression pattern consists of a strong fluorescence in the salivary duct, the copper cells, the proventriculus and the visceral musculature of the midgut. A weaker signal can be detected in imaginal disks. In first instar larvae, the fluorescence appears to be restricted to the midgut. GFP expression observed in the reproductive tract of the male; in females, in ovaries (yolk of mature stages and musculature of the ovary sheath) and in the seminal receptacle. In many animals, the visceral musculature of the midgut is also fluorescent.