"Does anyone know how to do wholemount X-gal staining on
newly eclosed adult flies?"
Very young flies (or pupae once extracted from the puparium) ) can
be X-gal labelled by using the same protocol as for embryos, including
the heptane-fixative styep which presumably removes the waxy layer
that prevents penetration of the X-gal chemicals through the adult
cuticle. The protocol we use is described in Ghysen and O'Kane
Development 105, 35-52.