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Thanks Theo, that was what I had deduced, but it is prudent to confirm one's suspicions.
Incidentally, such dichoptism, particularly among males seems to be very widespread in certain insects, generally males of flying insects, and in particular in many Diptera, though also in unrelated orders. I don't suppose that anyone in the forum happens to know of any reason why? I have a private speculation, but I'd rather not mention it before hearing what others have to say, for fear of influencing any discussion.