Green’s Dictionary of Slang

gum-sucker n.1

[the proliferation of gum trees; ‘he term dates back to the early 19thC when it was a common habit for people to chew on balls of gum taken from acacia trees. That only Victorians did this seems well-nigh impossible, but somehow the sobriquet was attached to them’ AWM (1993)]
(Aus.)

a European native Australian (esp. a Victorian) or a Tasmanian.

Show quotations
[Aus]W. Howitt Two Years in Victoria (1855) I 24: If he had not been too ’cute to be bitten twice by the over-“cute” gum-suckers,’ as the native Victorians are called.
[Aus]Leader (Melbourne) 23 June 4/2: He also quoted specimens of colonial slang [...] including such phrases as ‘cornstalk’ and ‘gumsucker’.
[Aus]Bulletin (Sydney) 28 May 4/1: Tasmania is at last becoming civilised. A few Victorians have recently gone over there and shown the ‘gum-suckers’ a trick or two in mining.
[UK]‘Aus. Colloquialisms’ in All Year Round 30 July 67/2: A gum-sucker is a native of Tasmania, and owes his elegant nickname to the abundance of gum-trees in the Tasmanian forests.
Quiz (Adelaide) Dec. 26: Quiz will take good care that the innocent Australians are not fooled without a warning. Really L. and his accomplices must look upon gumsuckers as being pretty soft.
[UK]J.H.M. Abbott Tommy Cornstalk 2: Jealous of Victorian prowess in eucalyptus cultivation [...] the other Australians refer to the Victorian people collectively as ‘Gum-suckers’.
[Aus]Bulletin (Sydney) 11 July 26/3: The weekly League games were suspended in Melbourne while Gumsuckers and Croweaters discussed which owned the thick end of the stick, so to speak. [...] The South Australians had more dash [...]. Per contra, the Victorians’ passing was a thing of beauty.
[Aus]J. Doone Timely Tips For New Australians 18: GUM-SUCKER.—A Victorian.
[Aus]Baker Aus. Lang. 185: The many expressions we have developed to describe those who are Australians [...] cornstalk, cornstalker, gumsucker, Aussie.
[Aus]B. Wannan Fair Go, Spinner 175: They were not admired by the Croweaters and Cornstalks and Gumsuckers.
[Aus]Aus. Word Map 🌐 gum suckers. Everyone from Victoria:.
[Aus]G. Seal Lingo 11: The usually derisive new chum is still hard occasionally (unlike another early synonym, gumsucker. [Ibid.] 33: gumsuckers is also a term for Victorians.