On page 237, Dewitt writes: "Metrodorus, a more impetuous individual than the master, afforded exceptional opportunities to the adversary. In some publication he had written: "The pleasure of the stomach is the beginning and root of all good, and the things of wisdom and the refinements of life have their standard of reference in this." (cites to Usener's Epicurea, 409).
However that statement does not seem to be attributed to Metrodorus by other commentators. such as here: http://monadnock.net/epicurus/fragments.html
This is from page 387 of Bailey's Extant Remains:
This too is relevant, but doesn't answer this particular question:
More from Bailey - who are Duen and Korte?
Also -
DeWitt spoke very highly of Bignone in his book (in the introduction, if I recall) so perhaps picked this attribution up from Bignone(?)
Probably it is not a major issue as to which of them said it, as either could have, but if this is an error in DeWitt it would be good to track it down.