Characteristic details of Colias crocea and Colias erate

In males Colias crocea butterflies, the androconial patch is an oval area located on the upper surface of the hindwing (UPH); this area is not clearly seen in flight.

This patch is present in males and contains specialised scent scales (androconia) which produce and release pheromones used to attract females during courtship. The presence and specific characteristics of these androconia and their patches can be used as a taxonomic feature to help distinguish Colias crocea from similar species, like Colias erate. 

The presence of this features is not conclusive; as you can see in John et al (2006)  a sex brand is also found in a small percentage of Colias erate. 

See below one photo of Colias crocea in flight with androconia seen, two photos of Colias crocea in flight whithout seen the androconia and one found dead in the ground, in which this androconia are indicated with a red arrow: