Three reputed MS-13 members pleaded not guilty on Tuesday to charges that they knifed a 16-year-old rival gang member to death in May 2017 in a wooded area of Queens.

Melvi Amador-Rios, 28; Josue Leiva, 22; and Luis Rivas, 24, were all already locked up on other charges when the feds unsealed an indictment on Sept. 12 charging them with killing Julio Vasquez in Alley Pond Park near 76th Avenue.

His body was discovered by a 52-year-old birdwatcher.

All three defendants appeared in Brooklyn federal court before Magistrate Judge Robert Levy wearing tan jail scrubs to enter their not guilty pleas. Tattoos covered Amador-Rios’ forearms and neck, as well as Leiva’s forearms.

Amador-Rios, alleged to be the head of the MS-13’s Centrales Locos Salvatruchas clique, has been behind bars since last year on charges that he put out an unsuccessful hit on a rival gang member.

Leiva was hit with robbery and firearms charges in March, and Rivas has been charged with assaulting a fellow inmate at a Manhattan lock-up while he was being held there for an attempted murder charge.