It was in the fall of 1958 that the Empire State Grenadiers and Berkshire Marauders merged to become the Interstatesmen. 

Mid-Sixties Interstatesmen Write-up on

Historical Drum Corps Publications

Article on Middle Horn Leader,

crediting Dom Delra and I-Men, for the Mellophone Bugle

(scroll down about 2/3rds of the page, for the section: EVOLUTION OF THE ....MELLOPHONE BUGLE)