How to sex the larvae of Cetoniidae and Dynastidae
It is a very simply method, everybody can do it!
On the ventral side of the last abdominal segment is a small black spot, called Herold's organ. This black spot has males. Females are without the spot. To see the Herold's organ is very easy, when the larvae are in third stage (L3). Of course, you can see it when they are younger too.
On the ventral side of the second or third abdominal segment is a small darker yellowish or brown triangel, which you can see, when the larvae are in third stage (L3). But it's more exacting to find the organ as by the Cetoniidae. Again has the Herold's organ only males.
How to sex adult Cetoniidae
Most of Flower beetles (males) has a dicranium or other prominency on the frontal side of head. But it's not so often easy, as you can think about it. Some males hasn't this garnish. So how to sex this adult beetles?
Usually has some adult males gains, which you can see on sternits.
Adult pair of Pachnoda.