Green’s Dictionary of Slang

bug n.2

[? SE bugger]

a man who incites homosexuals to join him in illegal pleasures.

[UK]J. Dalton Narrative of Street-Robberies 31: One night, he met with one ---, alias Susannah Haws, a Man who was what they call a Bug to the Mollies.
[UK]Satirist (London) 26 Aug. 278/4: On the signal for a charge be given, Sir Edward sounded the bug-le, and was answered by Cornuti Ellenborough’s horn.