Throwing out the following comment just to play safe -
Could it be Arcte coerula instead as:
1. A. modesta has not been reported from China before and
2. Some individuals of A. coerula also have blue scaling on the forewing.
pros and cons.
distribution is no longer a given, due to the large number of species shifting their global distributions as the effects of climate change take place. In Hong Kong, at least 70 nominally tropical species have been recorded (and some become established) since I finished my PhD in 2003.
More importantly for differentiating between coerula and modesta would be to see the hindwing. In modesta there is only one blue fascia, whereas in coerula there are three.
I have not added modesta to my database of Hong Kong moth species, but it is worth checking individuals of Arcte species encountered in Hong Kong.
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