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Chrysomelidae..two species..o sexual dimorphism..?
Chrysomelidae, Cassidinae, Mesomphaliini, Chelymorpha alternans.
https://www.flickr.com/photos/pasha_k/96...
It's a species of Chelymorpha. They are often extremely variable in their pattern (even more than coccinellids). So it's probably not a case of sexual dimorphism, rather polymorphism.
See pictures here: http://www.biol.uni.wroc.pl/cassidae/kat...
I am not familiar with dimorphism in chrysomelidae.
I have seen images of loose couplings between different species but do not think they get too serious.
Either way, it is an excellent spotting.