As promised in my reply to Henry's comment on the BC blog LH article on C. acalle, here is a a comparison pic (animated gif) of the male C. acalle (bottom) and C. trichopepla (top). Besides the difference in color and contrast of the HW discal patch against the ground colour, one consistent difference I observed is in the lowest spot of the discal path (highlighted with a white outline for both specimens).
For C. trichopepla, this spot is smaller and has "concave" black outline (the same feature is found in some Telicota spp.) whereas for C. acalle, this spot is bigger and has "pointed" forward outline.
Note that this is just my observation, and this difference has not been documented as an ID key for either species.
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